U.S. patent number 8,163,531 [Application Number 13/214,979] was granted by the patent office on 2012-04-24 for purification of vaccinia viruses using hydrophobic interaction chromatography.
This patent grant is currently assigned to Bavarian Nordic A/S, Otto-von-Guericke-Universitat, Sartorius Stedim Biotech GmbH. Invention is credited to Rene Faber, Anders Peter Gram, Sara Post Hansen, Udo Reichl, Michael Wolff.
United States Patent |
8,163,531 |
Post Hansen , et
al. |
April 24, 2012 |
**Please see images for:
( Certificate of Correction ) ** |
Purification of vaccinia viruses using hydrophobic interaction
chromatography
Abstract
The present invention relates to methods for purification of
Vaccinia viruses (VV) and/or Vaccinia virus (VV) particles, which
can lead to highly pure and stable virus preparations of
predominantly biologically active viruses. The invention
encompasses purifying a virus preparation in a sterilized way with
high efficiency and desirable yield in terms of purity, biological
activity and stability, aspects advantageous for industrial
production.
Inventors: |
Post Hansen; Sara (Hoersholm,
DK), Faber; Rene (Gottingen, DE), Reichl;
Udo (Magdeburg, DE), Wolff; Michael (Biederitz,
DE), Gram; Anders Peter (Vaerloese, DK) |
Assignee: |
Bavarian Nordic A/S
(Kvistgaard, DK)
Otto-von-Guericke-Universitat (Magdeburg, DE)
Sartorius Stedim Biotech GmbH (Gottingen,
DE)
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Family
ID: |
42165394 |
Appl.
No.: |
13/214,979 |
Filed: |
August 22, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110306114 A1 |
Dec 15, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12622563 |
Nov 20, 2009 |
8003364 |
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12622474 |
Nov 20, 2009 |
8003363 |
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12598362 |
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8012738 |
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PCT/EP2008/003679 |
May 7, 2008 |
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60924413 |
May 14, 2007 |
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Current U.S.
Class: |
435/239;
424/232.1; 424/199.1 |
Current CPC
Class: |
C12N
7/00 (20130101); A61P 37/04 (20180101); A61P
31/20 (20180101); C12N 7/02 (20130101); C12N
15/86 (20130101); C12N 2710/24143 (20130101); C12N
2710/24151 (20130101); A61K 2039/5256 (20130101) |
Current International
Class: |
C12N
7/02 (20060101); A61K 39/295 (20060101) |
References Cited
[Referenced By]
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Primary Examiner: Mosher; Mary E
Attorney, Agent or Firm: Law Office of Salvatore Arrigo and
Scott Lee, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No.
12/622,563, filed Nov. 20, 2009 now U.S. Pat. No. 8,003,364, which
is a continuation-in-part of U.S. application Ser. No. 12/622,474,
filed Nov. 20, 2009 now U.S. Pat. No. 8,003,363, which is a
continuation-in-part of U.S. application Ser. No. 12/598,362, filed
Oct. 30, 2009 now U.S. Pat. No. 8,012,738, which is the U.S.
National Stage of International Application No. PCT/EP2008/003679
filed May 7, 2008, which claims the benefit of U.S. Provisional
Application No. 60/924,413, filed May 14, 2007, all of which are
incorporated herein by reference.
Claims
We claim:
1. An industrial-scale method for the purification of biologically
active Vaccinia viruses comprising: i) binding the Vaccinia viruses
to a solid-phase sulfated cellulose matrix; ii) eluting the
Vaccinia viruses; iii) binding the eluted Vaccinia viruses to a
solid-phase hydrophobic interaction chromatograpy (HIC) matrix
comprising a phenyl ligand; and iv) eluting a minimum of
5.0.times.10.sup.12 Vaccinia virus particles.
2. The method of claim 1, wherein the method is performed under
aseptic conditions.
3. The method of claim 1, wherein the sulfated cellulose matrix
comprises a sulfated reinforced cellulose membrane.
4. The method of claim 3, wherein the method is performed under
aseptic conditions.
5. The method of claim 1, wherein the Vaccinia viruses are
recombinant Vaccinia virus.
6. The method of claim 1, wherein the Vaccinia viruses are modified
Vaccinia Ankara viruses or recombinant modified Vaccinia Ankara
viruses.
7. The method of claim 6, wherein the method is performed under
aseptic conditions.
8. The method of claim 1, wherein the Vaccinia viruses are eluted
from the sulfated cellulose matrix with ammonium sulfate.
9. The method of claim 8, wherein the Vaccinia viruses are eluted
from the sulfated cellulose matrix with 1.7 M ammonium sulfate.
10. The method of claim 1, wherein the Vaccinia viruses are eluted
from the HIC matrix with a citric acid buffer.
11. The method of claim 1, further comprising a purification step
by ion-exchange.
12. The method of claim 11, wherein the method is performed under
aseptic conditions.
13. The method of claim 2, further comprising administering the
eluted Vaccinia virus to an animal.
14. The method of claim 13, wherein the animal is a human.
15. An industrial-scale method for the purification of biologically
active Vaccinia viruses comprising: i) binding the Vaccinia viruses
to a solid-phase heparin ligand matrix; ii) eluting the Vaccinia
viruses; iii) binding the eluted Vaccinia viruses to a solid-phase
hydrophobic interaction chromatograpy (HIC) matrix comprising a
phenyl ligand; and iv) eluting a minimum of 5.0.times.10.sup.12
Vaccinia virus particles.
16. The method of claim 15, wherein the method is performed under
aseptic conditions.
17. The method of claim 15, wherein the heparin ligand matrix
comprises a heparin ligand membrane.
18. The method of claim 17, wherein the method is performed under
aseptic conditions.
19. The method of claim 15, wherein the Vaccinia viruses are
recombinant Vaccinia viruses.
20. The method of claim 15, wherein the Vaccinia viruses are
modified Vaccinia Ankara viruses or recombinant modified Vaccinia
Ankara viruses.
21. The method of claim 1, wherein the sulfated cellulose matrix is
a sulfated reinforced cellulose membrane.
22. The method of claim 15, wherein the heparin ligand matrix is a
heparin ligand membrane.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to methods for purification of Vaccinia
viruses (VV) and/or Vaccinia virus (VV) particles.
2. Description of Related Art
Traditionally in medicine, a vector is a living organism that does
not cause disease itself, but which spreads infection by "carrying"
pathogens (agents that cause disease) from one host to another. A
vaccine vector is a weakened or killed version of a virus or
bacterium that carries an inserted antigen (coding for a protein
recognized by the body as foreign) from a disease-causing agent to
the subject being vaccinated. A vaccine vector delivers the antigen
in a natural way into the body and stimulates the immune system
into acting against a "safe infection." The immune system is led
into generating an immune response against the antigen that
protects the vaccinated subject against future "risky
infections."
In vaccine development, a recombinant modified virus can be used as
the vehicle or vaccine vector for delivering genetic material to a
cell. Once in the cell, genetic information is transcribed and
translated into proteins, including the inserted antigen targeted
against a specific disease. Treatment is successful if the antigen
delivered by the vector into the cell produces a protein, which
induces the body's immune response against the antigen and thereby
protects against the disease.
A viral vector can be based on an attenuated virus, which cannot
replicate in the host but is able to introduce and express a
foreign gene in the infected cell. The virus or the recombinant
virus is thereby able to make a protein and display it to the
immune system of the host. Some key features of viral vectors are
that they can elicit a strong humoral (B-cell) and cell-mediated
(T-cell) immune response.
Viral vectors are commonly used by researchers to develop vaccines
for the prevention and treatment of infectious diseases and cancer,
and of these, poxviruses (including canary pox, vaccinia, and fowl
pox) are the most common vector vaccine candidates.
Pox viruses are a preferred choice for transfer of genetic material
into new hosts due to the relatively large size of the viral genome
(appr. 150/200 kb) and because of their ability to replicate in the
infected cell's cytoplasm instead of the nucleus, thereby
minimizing the risk of integrating genetic material into the genome
of the host cell. Of the pox viruses, the vaccinia and variola
species are the two best known. The virions of pox viruses are
large as compared to most other animal viruses (for more details
see Fields et al., eds., Virology, 3.sup.rd Edition, Volume 2,
Chapter 83, pages 2637 ff).
Variola virus is the cause of smallpox. In contrast to variola
virus, vaccinia virus does not normally cause systemic disease in
immune-competent individuals and it has therefore been used as a
live vaccine to immunize against smallpox. Successful worldwide
vaccination with Vaccinia virus culminated in the eradication of
smallpox as a natural disease in the 1980s (The global eradication
of smallpox. Final report of the global commission for the
certification of smallpox eradication; History of Public Health,
No. 4, Geneva: World Health Organization, 1980). Since then,
vaccination has been discontinued for many years, except for people
at high risk of poxvirus infections (for example, laboratory
workers). However, there is an increasing fear that, for example,
variola causing smallpox may be used as a bio-terror weapon.
Furthermore, there is a risk that other poxviruses such as cowpox,
camelpox, and monkeypox may potentially mutate, through selection
mechanisms, and obtain similar phenotypes as variola. Several
governments are therefore building up stockpiles of Vaccinia-based
vaccines to be used either pre-exposure (before encounter with
variola virus) or post-exposure (after encounter with variola
virus) of a presumed or actual smallpox attack.
Vaccinia virus is highly immune-stimulating and provokes strong B-
(humoral) and T-cell mediated immunity to both its own gene
products and to any foreign gene product resulting from genes
inserted in the Vaccinia genome. Vaccinia virus is therefore seen
as an ideal vector for vaccines against smallpox and other
infectious diseases and cancer in the form of recombinant vaccines.
Most of the recombinant Vaccinia viruses described in the
literature are based on the fully replication competent Western
Reserve strain of Vaccinia virus. It is known that this strain has
a high neurovirulence and is thus poorly suited for use in humans
and animals (Morita et al. 1987, Vaccine 5, 65-70).
In contrast, the Modified Vaccinia virus Ankara (MVA) is known to
be exceptionally safe. MVA has been generated by long-term serial
passages of the Chorioallantois Vaccinia Ankara (CVA) strain of
Vaccinia virus on chicken embryo fibroblast (CEF) cells (for review
see Mayr, A. et al. 1975, Infection 3, 6-14; Swiss Patent No.
568,392). Examples of MVA virus strains deposited in compliance
with the requirements of the Budapest Treaty are strains MVA 572,
MVA 575, and MVA-BN.RTM. deposited at the European Collection of
Animal Cell Cultures (ECACC), Salisbury (UK) with the deposition
numbers ECACC V94012707, ECACC V00120707 and ECACC V00083008,
respectively, and described in U.S. Pat. Nos. 7,094,412 and
7,189,536.
MVA is distinguished by its great attenuation profile compared to
its precursor CVA. It has diminished virulence or infectiousness,
while maintaining good immunogenicity. The MVA virus has been
analyzed to determine alterations in the genome relative to the
wild type CVA strain. Six major deletions of genomic DNA (deletion
I, II, III, IV, V, and VI) totaling 31,000 base pairs have been
identified (Meyer, H. et al. 1991, J. Gen. Virol. 72, 1031-1038).
The resulting MVA virus became severely host-cell restricted to
avian cells. The excellent properties of the MVA strain have been
demonstrated in extensive clinical trials (Mayr, A. et al. 1978,
Zbl. Bakt. Hyg. I, Abt. Org. B 167, 375-390; Stickl, H. et al.
1974, Dtsch. med. Wschr. 99, 2386-2392), where MVA 571 has been
used as a priming vaccine at a low dose prior to the administration
of conventional smallpox vaccine in a two-step program and was
without any significant adverse events (SAES) in more than 120,000
primary vaccinees in Germany (Stickl, H et al. 1974, Dtsch. med.
Wschr. 99, 2386-2392; Mayr et al. 1978, Zbl. Bakt. Hyg. I, Abt.
Org. B 167, 375-390).
MVA-BN.RTM. is a virus used in the manufacturing of a stand-alone
third generation smallpox vaccine. MVA-BN.RTM. was developed by
further passages from MVA strain 571/572. To date, more than 1500
subjects including subjects with atopic dermatitis (AD) and HIV
infection have been vaccinated in clinical trials with MVA-BN.RTM.
based vaccines.
The renewed interest in smallpox vaccine-campaigns with
Vaccinia-based vaccines has initiated an increased global demand
for large-scale smallpox vaccine production. Furthermore, the use
of Vaccinia virus as a tool for preparation of recombinant vaccines
has additionally created significant industrial interest in methods
for manufacturing (growth and purification) of native Vaccinia
viruses and recombinant-modified Vaccinia viruses.
Viruses used in the manufacturing of vaccines or for diagnostic
purposes can be purified in several ways depending on the type of
virus. Traditionally, purification of pox viruses including
Vaccinia viruses and recombinant-modified Vaccinia viruses has been
carried out based on methods separating molecules by means of their
size differences. To enhance removal of host cell contaminants
(e.g. DNA and proteins), in particular DNA, the primary
purification by means of size separation has been supplemented by
secondary methods such as enzymatic digestion of DNA (e.g.
Benzonase treatment). Most commonly, the primary purification of
Vaccinia viruses and recombinant-modified Vaccinia viruses has been
performed by sucrose cushion or sucrose gradient centrifugation at
various sucrose concentrations. Recently, ultrafiltration has also
been applied either alone or in combination with sucrose cushion or
sucrose gradient purification.
Vaccinia Viruses-based vaccines have in general been manufactured
in primary CEF (Chicken Embryo Fibroblasts) cultures. Vaccines
manufactured in primary CEF cultures are generally considered safe
as regards residual contaminants. First, it is scientifically
unlikely that primary cell cultures from healthy chicken embryos
should contain any harmful contaminants (proteins, DNA). Second,
millions of people have been vaccinated with vaccines manufactured
on CEF cultures without any adverse effects resulting from the
contaminants (CEF proteins and CEF DNA). There is, therefore, no
regulatory requirement for the level of host cell contaminants in
vaccines manufactured in primary CEF cultures, but for each vaccine
the manufacturer must document its safety. The regulatory concern
for vaccines manufactured in primary CEF cultures relates to the
risk of adventitious agents (microorganisms (including bacteria,
fungi, mycoplasma/spiroplasma, mycobacteria, rickettsia, viruses,
protozoa, parasites, TSE agent) that are inadvertently introduced
into the production of a biological product).
In the current methods for purification of Vaccinia viruses,
manufactured in primary CEF culture the level of CEF protein may be
up to 1 mg/dose and the CEF DNA level may exceed 10 .mu.g/dose of
1.times.10.sup.8 as measured by the TCID50. These levels are
considered acceptable from a safety and regulatory perspective as
long as the individual vaccine manufacturer demonstrates that the
levels to be found in the Final Drug Product (FDP) are safe at the
intended human indications. Due to the risk of presence of
adventitious agents in vaccines manufactured in primary cell
cultures and the associated need for extensive, expensive biosafety
testing of each vaccine batch manufactured, there is a strong
stimulus for the vaccine industry to change to continuous cell
lines. Once a continuous cell line has been characterized, the need
for testing for adventitious agents of the production batches is
minimal.
However, switch from primary to continuous cell culture for
production of Vaccinia and Vaccinia recombinant vaccines is
expected to impose stricter safety and regulatory requirements. In
fact, the regulatory authorities have proposed new requirements for
levels of DNA contaminants in vaccines manufactured using
continuous cell lines (See Draft FDA guideline), which may be as
low as 10 .mu.g host-cell DNA/dose. To achieve such low level of
host cell contaminants, new and improved methods for purification
are needed.
It appears that vaccinia virions are able to bind to heparin
through the surface protein A27L (Chung et al. 1998, J. Virol. 72,
1577-1585). At least three surface proteins A27L (Chung et al., J.
Virol. 72(2):1577-1585, 1998; Ho et al., Journal of Molecular
Biology 349(5):1060-1071, 2005; Hsiao et al., J. Virol.
72(10):8374-8379, 1998) D8L (Hsiao et al., J. Virol.
73(10):8750-8761, 1999), and H3L (Lin et al., J. Virol.
74(7):3353-3365, 2000) of the most abundant infectious form of the
Vaccinia virus have been reported to bind to
glycosaminoglycans.
Examples of glycosaminoglycans in affinity chromatography
applications are heparin and heparan sulfate. These are highly
charged, linear and sulfated polysaccharides composed of repeating
disaccharide units containing an uronic acid (glucuronic or
iduronic acid) and an N-sulfated or N-acetylated glucosamine
(Ampofo et al., Analytical Biochemistry 199(2):249-255, 1991;
Nugent, Proceedings of the National Academy of Sciences of the
United States of America 97(19):10301-10303, 2000; Rabenstein, Nat.
Prod. Rep. 19:312-331, 2002).
Cellufine.RTM. sulfate and sulfated cellulose membranes are
sulfated glucose polymers. Several studies reported antiviral
activities of sulfated cellulose and sulfated dextran/dextrines
(Baba et al., Antimicrob. Agents Chemother. 32(11):1742-1745, 1988;
Chattopadhyay et al., International Journal of Biological
Macromolecules 43(4):346-351, 2008; Mitsuya et al., Science
240(4852):646-649, 1988; Piret et al., J. Clin. Microbiol.
38(1):110-119, 2000), as well as the binding of virus particles to
Cellufine.RTM. sulfate (O'Neil et al., Bio/Technology 11:173-178,
1993; Opitz et al., Biotechnol. and Bioeng. 103(6):1144-1154,
2009). The precise interaction between these viruses and sulfated
cellulose is currently not fully understood.
It has further been suggested that affinity chromatography (Zahn, A
and Allain, J.-P. 2005, J. Gen. Virol. 86, 677-685) may be used as
basis for purification of certain virus preparations. There are
several examples for the application of ion exchange and affinity
membrane adsorbers (MA) for the purification of virus particles
like adenoviral vectors (Peixoto et al., Biotechnology Progress
24(6):1290-1296, 2008; Sellick, BioPharm International 19(1):31-32,
34, 2006), Aedes aegyptidensonucleosis virus (Enden et al., J Theor
Biol 237(3):257-264, 2005), baculovirus (Wu et al., Hum. Gene Ther.
18(7):665-672, 2007), and influenza virus (Kalbfuss et al., Journal
of Membrane Science 299(1-2):251-260, 2007; Opitz et al.,
Biotechnol. and Bioeng. 103(6):1144-1154, 2009; and Opitz et al.,
Journal of Biotechnology 131(3):309-317, 2007).
For efficient purification of vaccinia virus and recombinant
vaccinia virus-based vaccines, some significant challenges need to
be overcome. Vaccinia virions are far too large to be effectively
loaded onto commercially available heparin columns, e.g., the
Hi-Trap heparin column from Amersham Biosciences used by others
(Zahn, A and Allain, J.-P. 2005, J. Gen. Virol. 86, 677-685) for
lab-scale purification of Hepatitis C and B viruses. The Vaccinia
virion volume is approximately 125 times larger than Hepatitis
virion. (The diameter of the Vaccinia virus is, thus, appr. 250 nm
as compared with the hepatitis C and B virions diameter being appr.
50 nm). Thus, available matrices as, e.g., used in the column-based
approach may not allow for adequate entrance of virions into the
matrix, loading of sufficient amounts of virus particles or
sufficiently rapid flow through the column to meet the needs for
industrial scale purification. Zahn and Allain worked with virus
load up to 1.times.10.sup.6 in up to 1.0 ml volume. For pilot-scale
purification to achieve sufficient material for early clinical
trials virus loading capacity higher than 1.times.10.sup.11,
preferably up 1.times.10.sup.13, in volumes higher than 5 L,
preferably up to 50 L, is needed. For industrial purification of
Vaccinia virus loading capacity higher than 1.times.10.sup.13,
preferably higher than 1.times.10.sup.14 in volumes higher than 300
L, preferably higher than 600 L, is needed.
The large size of the Vaccinia virus may prevent effective steric
access between the specific surface proteins of the virions and the
ligand immobilized to the matrix. Currently described lab-scale
methods of use for purification of small virus particles may
therefore not be industrially applicable to purification of
Vaccinia virus.
Due to the high number of functional surface molecules interacting
with the ligand used for binding of the Vaccinia virus particles,
elution of bound Vaccinia virus may require more harsh and
therefore potentially denaturing conditions to elute and recover
the Vaccinia virus particles in a biologically effective form in
high yields. The matrix, the ligand design, the method of ligand
immobilization, and the ligand density may therefore require
careful design to mediate an effective binding of the Vaccinia
virus and to permit an effective elution of biologically active
Vaccinia virus particles.
Vaccinia virions are too large to be sterile filtered. The method
used in this invention has therefore been developed by to be
applicable for an aseptic industrial-scale manufacturing process in
a way ensuring full compliance with regulatory requirements
regarding sterility of vaccines. In line with the above and for the
purpose of this invention, the column substituted with the ligand
can be applicable for sterilization-in-place or can be available as
a pre-sterilized unit.
In the past, numerous methods like cesium chloride gradient
centrifugation (Payne and Norrby 1976), sucrose cushion or sucrose
gradient centrifugation (Esteban and Metz 1973; Joklik 1962;
Madalinski et al. 1977; Zwartouw et al. 1962), tangential-flow
filtration and diafiltration (Greenberg and Kennedy 2008; Monath et
al. 2004), as well as size exclusion chromatography (Stickl et al.
1970), have been described for the isolation and purification of
smallpox virus particles. Introduction of cell culture-derived
smallpox vaccines production processes led to a reconsideration of
the classic purification schemes.
Current smallpox vaccines are purified mainly after cell disruption
by centrifugation and filtration methods (Abdalrhman et al. 2006;
Greenberg and Kennedy 2008; Monath et al. 2004). However, residual
DNA levels need to be further reduced for newly licensed vaccine
products from continuous cell lines to comply with current
regulations. Accordingly, biopharmaceutical product solutions used
for injection should contain less than 10 ng of cellular DNA per
dose (World-Health-Organization 1998) to reduce the possibilities
for cellular transformations by potential oncogenic DNA
(Sheng-Fowler et al. 2009) and infections by infectious DNA. Hence,
DNA contaminants need to be reduced, which is commonly done for
smallpox and other vaccines, as well as for viral vectors, by
nuclease treatments (Greenberg and Kennedy 2008; Konz et al. 2005;
Monath et al. 2004; Transfiguracion et al. 2003; Wolff and Reichl
2008).
Alternative approaches described in the literature for the
clearance of host cell DNA from biopharmaceutical products are
density gradient centrifugation, precipitation, anion exchange and
affinity chromatography. For example Kumar et al. (Kumar et al.
2002) demonstrated the clearance of host cell DNA from rabies
vaccine by density gradient centrifugation. Selective precipitation
has been described for the preparation of poliovaccines (Amosenko
et al. 1991) and recombinant adenoviral vectors (Goerke et al.
2005). Chromatographic approaches are frequently applied for DNA
reductions in recombinant protein production processes (Gagnon et
al. 2006; Knudsen et al. 2001; Sakata and Kunitake 2007; Sakata et
al. 2005; Tauer et al. 1995) and viral vaccines (Kalbfuss et al.
2007; Opitz et al. 2009; Opitz et al. 2008). Recently, a downstream
scheme focusing on a sequential combination of pseudo-affinity and
anion exchange membrane adsorbers (MA) has been described (Wolff et
al. 2009) allowing a significant reduction of DNA in cell
culture-derived smallpox vaccines. However, the DNA burden needs to
be still improved. Hydrophobic interaction chromatography (HIC) is
routinely used in bioseparations (Graumann and Ebenbichler 2005;
Kramarczyk et al. 2008; Lu et al. 2009; Mahn and Asenjo 2005;
Queiroz et al. 2001; Tsumoto et al. 2007; Ueberbacher et al. 2008)
since it offers an orthogonal separation technique to purification
methods based on ionic interactions. HIC is influenced by many
factors like ligands, ligand densities, applied salts, pH, buffer
type and temperature (Graumann and Ebenbichler 2005; Kramarczyk et
al. 2008; Queiroz et al. 2001).
The influence of salts on hydrophobic interactions follows the
lyotropic (Hofmeister) series according to their effect on the
solubility of macromolecules in aqueous solutions (Graumann and
Ebenbichler 2005; Kramarczyk et al. 2008; Queiroz et al. 2001).
Antichaotropic salts are considered to be water structuring,
whereas chaotropic ions randomize liquid water structure and those
are likely to reduce the hydrophobic interaction strength (Queiroz
et al. 2001). In recent years HIC gained popularity for the
separation of plasmid DNA from impurities like RNA, genomic DNA,
lipopolysaccharides and denatured plasmid forms (Diogo et al.
2000).
To achieve a bio-specific purification of Vaccinia virus particles
with high biological activity, there is a need in the art for
development of industrially usable ligands for Vaccinia virus
purification. Thus, use of a ligand displaying highly specific and
highly effective binding to the Vaccinia virus would be
advantageous as it would improve purification by its ability to
specifically sort out biologically active Vaccinia virus particles
thereby increasing the purity, viability, and functionality of the
purified Vaccinia virus.
BRIEF SUMMARY OF THE INVENTION
The invention encompasses methods for virus purification. The
application of adsorption chromatography to capture virus particles
after cell homogenization and cell debris clearance is described.
The invention includes virus purification using pseudo-affinity
chromatography based on heparin and sulfated cellulose and/or
hydrophobic interaction chromatography based on ether,
poly-propylene-glycol, phenyl, butyl, or hexyl functional
groups.
A hydrophobic interaction chromatography media was used to reduce
the DNA content of virus preparations. Several different
hydrophobic interaction chromatography ligands were analyzed.
Pseudo-affinity membrane adsorbers, based on reinforced sulfated
cellulose and heparin-membrane adsorbers, were also used. These
were optimized in terms of dynamic binding capacities and
contaminant depletion
The combination of sulfated cellulose membrane adsorbers with a
phenyl hydrophobic interaction chromatography resulted in an
overall virus recovery range of 76% to 55%. DNA depletion was
reduced to 0.01% of the initial starting material and the reduction
of total protein achieved a protein contamination below 0.1%.
The invention encompasses methods for purifying biologically active
Vaccinia viruses. In one embodiment, the method comprises loading a
solid-phase matrix, to which a ligand is attached, with a
biologically active Vaccinia virus contained in a liquid-phase
culture, washing the matrix; and eluting the biologically active
Vaccinia virus.
In one embodiment, the invention encompasses a method for the
purification of biologically active Vaccinia virus comprises
binding the Vaccinia virus to a solid-phase hydrophobic interaction
chromatograpy (HIC) matrix and eluting the biologically active
virus. In one embodiment, the method further comprises binding the
Vaccinia virus to a solid-phase pseudo-affinity (PA) matrix; and
eluting the biologically active virus.
In one embodiment, the binding the Vaccinia virus to the PA matrix
is performed prior to binding the Vaccinia virus to the HIC matrix.
In one embodiment, the binding the Vaccinia virus to the HIC matrix
is performed prior to binding the Vaccinia virus to the PA
matrix.
Preferably, the HIC matrix comprises a PPG ligand, a phenyl ligand,
a butyl ligand, or a hexyl ligand.
In one embodiment, the eluted Vaccinia virus contains less than 10
ng host-cell DNA per 10.sup.8 virus particles. In one embodiment,
the method reduces the amount of dsDNA in the eluted virus to less
than 0.04% of input. In one embodiment, the method reduces the
amount of dsDNA in the eluted virus to less than 0.1% of input.
In one embodiment, the PA matrix comprises or is a membrane.
Preferably, the PA matrix comprises or is a sulfated cellulose
matrix. More preferably, the sulfated cellulose matrix comprises or
is a sulfated reinforced cellulose membrane.
In one embodiment, the PA matrix comprises or is a heparin ligand
membrane.
In one embodiment, the Vaccinia virus is a recombinant Vaccinia
virus. In one embodiment, the Vaccinia virus is MVA or recombinant
MVA.
In one embodiment, the Vaccinia virus is eluted from the PA matrix
with ammonium sulfate. In a preferred embodiment, the Vaccinia
virus is eluted from the PA matrix with 1.7 M ammonium sulfate.
In one embodiment, the Vaccinia virus is eluted from the HIC matrix
with a citric acid buffer.
In one embodiment, the method further comprises a purification step
by ion-exchange.
In one embodiment, the purified Vaccinia virus retains at least 30%
of its initial TCID50.
In one embodiment, the method further comprises administering the
eluted Vaccinia virus to an animal, preferably a human.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts screening of hydrophobic interaction chromatography
media. Relative amounts of virus (MVA, ELISA), total dsDNA (DNA;
Quant-iT.RTM. PicoGreen.RTM. assay) and total protein (P;
Pierce.RTM. BCA protein assay) during the purification of CEF
cell-derived MVA-BN.RTM. virus particles using 1 ml columns of
ToyoScreen.RTM. Ether, ToyoScreen.RTM. PPG, ToyoScreen.RTM. Phenyl,
ToyoScreen.RTM. Butyl and ToyoScreen.RTM. Hexyl. Adsorption buffer:
1.7 M (NH4)2SO4, 50 mM K2HPO4, pH 7.4; elution buffer: 50 mM
K2HPO4, pH 7.4. All chromatographic experiments were conducted 3
times and the individual samples were analyzed as described in the
material and method section; error bars: mean and standard
deviation of each test series.
FIG. 2 depicts purification of MVA-BN.RTM. (batch A) by a
combination of a SC-MA (15 layers, d=25 mm, A=75 cm.sup.2) or
heparin-MA (3.times.15 layers, d=25 mm, A=225 cm.sup.2) with a 1 ml
HIC-phenyl column (ToyoScreen.RTM. Phenyl-650M). The loading and
equilibration buffer for the SC-MA and heparin-MA was 100 mM citric
acid, pH 7.4 and the elution buffer 1.7 M (NH.sub.4).sub.2SO4, 50
mM K.sub.2HPO.sub.4, pH 7.4. The loading and equilibration buffer
for the HIC-phenyl column corresponded to the elution buffer of the
pseudo-affinity MA. The elution buffer of the HIC-phenyl column was
100 mM citric acid, pH 7.4. The flow rate for the entire process
was 1 ml/min. The relative virus content was monitored by an ELISA;
relative amounts of total protein and dsDNA were quantified by the
Pierce.RTM. BCA protein assay and the Quant iT.TM. PicoGreen.RTM.
assay, respectively, based on the initially loaded amounts. All
chromatographic experiments were done in triplicates. The ELISA and
total protein analysis of individual samples were conducted in
triplicates and the dsDNA measurements in duplicates.
FIG. 3 depicts determination of the optimal salt concentration for
MVA-BN.RTM. adsorption to 1 ml ToyoScreen.RTM. Phenyl matrix.
Relative amounts of MVA-BN.RTM. virus particles (ELISA) in the flow
through and product fraction as well as total dsDNA (DNA;
Quant-iT.RTM. PicoGreen.RTM.) in the flow through and product
fraction. Adsorption buffer: 1.7, 1.5, 1.25, 1, 0.85, 0.6 and 0.45
M (NH.sub.4).sub.2SO.sub.4, 50 mM K.sub.2HPO.sub.4, pH 7.4; elution
buffer: 50 mM K.sub.2HPO.sub.4, pH 7.4. The chromatographic
experiments were conducted twice and individual samples were
analyzed in duplicates (dsDNA-assay) and triplicates (ELISA) as
described in the material and method section; error bars: mean and
standard deviation of each test series.
DETAILED DESCRIPTION OF THE INVENTION
The invention encompasses methods for purifying viruses. In
particular, the present invention is directed to a method for the
purification of biologically active Vaccinia virus comprising:
a. loading a solid-phase matrix, to which a ligand is attached,
with a Vaccinia virus contained in a liquid-phase culture;
b. washing the matrix, and
c. eluting the biologically active Vaccinia virus.
The ligand is a substance that, on the one hand, can be attached to
the solid-phase matrix, e.g., by binding or coupling thereto and
that, on the other hand, is able to form a reversible complex with
the Vaccinia virus. Thus, by interacting with the virus, the virus
is reversibly retained.
The ligand can be a biological molecule as, for example, a peptide
and/or a lectin and/or an antibody and/or, preferably, a
carbohydrate. The ligand may also comprise or consist of sulfate.
In a further embodiment, the ligand comprises one or more
negatively charged sulfate groups.
Preferably, the ligand is a hydrophobic molecule as, for example,
an aromatic phenyl group, a PPG group, a butyl group, or a hexyl
group.
In one embodiment, the method comprises purification of Vaccinia
virus with hydrophobic interaction chromatography (HIC). In a
further embodiment, the method comprises purification of Vaccinia
virus with HIC together with pseudo-affinity chromatography.
The use of HIC can provide high virus yields with large reductions
in DNA and protein contaminants. The level of DNA contamination can
be reduced to 0.01% of the initial starting material and the level
of protein contamination can be reduced to below 0.1%.
Combination of sulfated cellulose based MA with HIC phenyl column
chromatography allowed the purification of CEF cell culture-derived
MVA-BN.RTM. virus particles at high virus yields and impressive
purity levels. Protein levels were after SC-MA and HIC-phenyl
chromatography purification independent of the tested production
batch below 25 .mu.g total protein per dose. Hence, protein levels
would be sufficient for newly licensed cell culture-derived human
vaccine products.
Current guidelines for newly licensed human vaccine products from
continues cell lines dictate that residual DNA levels exceeding 10
ng per dose are not acceptable (Gijsbers et al. 2005; Sheng-Fowler
et al. 2009; World-Health-Organization 1998). DNA depletion was, in
some cases, sufficient to evade nuclease treatment. A further
Benzonase.RTM. treatment can be included. Due to the tremendously
reduced amount of DNA in the product fractions, the required amount
of Benzonase.RTM. for nuclease treatment can be tremendously
reduced allowing a cost-effective modification of current
downstream processes. Furthermore, a small scale Benzonase.RTM.
treatment reduces the probability of vaccines or viral vectors to
contain intact oncogenes or further functional DNA sequences.
The invention encompasses a process based on SC-MA in combination
with HIC-phenyl chromatography for a downstream process for
Vaccinia virus particles in a manufacturing process and allows for
economizing the required nuclease treatment step compared to
classical downstream processes for small pox vaccines or
MVA-BN.RTM. based viral vectors.
The ligand can be attached to the matrix directly, e.g, by direct
binding, or can be attached to the matrix indirectly though another
molecule, e.g. by coupling through a linker or spacer.
The solid-phase matrix can be a gel, bead, well, membrane, column,
etc. In a preferred embodiment of the invention, the solid-phase
comprises or is a membrane, in particular a cellulose membrane.
However, a broad range of other polymers modified with specific
groups capable to bind the virus can be used. Preferred are
hydrophilic polymers. Examples are cellulose derivatives (cellulose
esters and mixtures thereof, cellulose hydrate, cellulose acetate,
cellulose nitrate); agarose and its derivatives; other
polysaccharides like chitin and chitosan; polyolefines
(polypropylene); polysulfone; polyethersulfone; polystyrene;
aromatic and aliphatic polyamides; polysulfonamides; halogenated
polymers (polyvinylchloride, polyvinylfluoride,
polyvinylidenfluoride); polyesters; homo- and copolymers of
acrylnitrile.
The method and further embodiments of the invention can overcome
the limitations of currently known methods preventing
industrial-scale, effective purification of Vaccinia virus
particles with high biological activity and purity. The method is
superior in terms of yield, process time, purity, recovery of
biologically active Vaccinia virus particles and costs to existing
pilot-scale methods for purification of Vaccinia virus particles,
which are primarily based on sucrose-cushion centrifugation and/or
diafiltration or non-specific ion-exchange chromatography. It is
also superior in terms of yield, process time, purity, recovery of
biologically active Vaccinia virus particles, and costs to the only
existing large-scale method for purification of Vaccinia virus
particles, which is based on ultrafiltration, enzymatic DNA
degradation, and diafiltration.
According to the present invention, Vaccinia virus can be purified
under aseptic conditions to obtain a biologically active, stable,
and highly pure virus preparation in high yield. The Vaccinia
viruses can be native or recombinant.
The present invention provides an improved method for aseptic
purification of Vaccinia viruses in lab-, pilot-, and, preferably,
in industrial-scale, leading to a biologically active, stable and
highly pure virus preparation in high yield.
This invention provides a more time-effective and cost-effective
process for purification of Vaccinia viruses and recombinant
Vaccinia viruses, Modified Vaccinia virus Ankara (MVA) and
recombinant MVA, MVA-BN.RTM. and recombinant MVA-BN.RTM., leading
to a biologically active, stable and highly pure virus preparation
in high yield.
In another embodiment, this invention provides virus preparations
produced by the method of the invention.
Use of the eluted Vaccinia virus or recombinant Vaccinia virus, or
Modified Vaccinia virus Ankara (MVA) or recombinant MVA or
MVA-BN.RTM. or recombinant MVA-BN.RTM., all preferably obtained by
the method according to the present invention, for the preparation
of a pharmaceutical composition, in particular a vaccine, is also
an embodiment of the invention. The virus and/or pharmaceutical
preparation is preferably used for the treatment and/or the
prevention of cancer and/or of an infectious disease.
A method for inducing an immune response or for the vaccination of
an animal, specifically of a mammal, including a human, in need
thereof, characterized by the administration of a Vaccinia virus or
recombinant Vaccinia virus, or Modified Vaccinia virus Ankara (MVA)
or recombinant MVA or MVA-BN.RTM. or recombinant MVA-BN.RTM.
vaccine prepared by a process comprising a purification step as
described above is a further embodiment of the invention.
As used herein, an "attenuated virus" is a strain of a virus whose
pathogenicity has been reduced compared to its precursor, for
example by serial passaging and/or by plaque purification on
certain cell lines, or by other means, so that it has become less
virulent because it does not replicate, or exhibits very little
replication, but is still capable of initiating and stimulating a
strong immune response equal to that of the natural virus or
stronger, without producing the specific disease.
According to a further preferred embodiment of the present
invention, glucosamine glycan (GAG), in particular heparan sulfate
or heparin, or a GAG-like substance is used as ligand.
As used herein, "glycosaminoglycans" (GAGs) are long un-branched
polysaccharides consisting of a repeating disaccharide unit. Some
GAGs are located on the cell surface where they regulate a variety
of biological activities such as developmental processes, blood
coagulation, tumor metastasis, and virus infection.
As used herein, "GAG-like agents" are defined as any molecule which
is similar to the known GAGs, but can be modified, for example, by
the addition of extra sulfate groups (e.g. over-sulfated heparin).
"GAG-like ligands" can be synthetic or naturally occurring
substances. Additionally, the term "GAG-like ligands" also covers
substances mimicking the properties of GAGs as ligands in
ligand-solid-phase complexes. One example for a "GAG-like ligand"
mimicking GAG, specifically heparin, as ligand is Sulfate attached
to Reinforced Cellulose as solid-phase, thus forming Sulfated
Reinforced Cellulose (SRC) as ligand-solid-phase complex. The use
of SRC complex is also a preferred embodiment of the present
invention. Stabilized Reinforced Cellulose membranes can be
obtained, for example, from Sartorius AG.
As used herein, "Bulk Drug Substance" refers to the purified virus
preparation just prior to the step of formulation, fill and finish
into the final vaccine.
As used herein, "Biological activity" is defined as Vaccinia virus
virions that are either 1) infectious in at least one cell type,
e.g. CEFs, 2) immunogenic in humans, or 3) both infectious and
immunogenic. A "biologically active" Vaccinia virus is one that is
either infectious in at least one cell type, e.g. CEFs, or
immunogenic in humans, or both. In a preferred embodiment, the
Vaccinia virus is infectious in CEFs and is immunogenic in
humans.
As used herein, "contaminants" cover any unwanted substances which
may originate from the host cells used for virus growth (e.g. host
cell DNA or protein) or from any additives used during the
manufacturing process including upstream (e.g. gentamicin) and
downstream (e.g. Benzonase).
As used herein, "continuous cell culture (or immortalized cell
culture)" describes cells that have been propagated in culture
since the establishment of a primary culture, and they are able to
grow and survive beyond the natural limit of senescence. Such
surviving cells are considered as immortal. The term immortalized
cells were first applied for cancer cells which were able to avoid
apoptosis by expressing a telomere-lengthening enzyme. Continuous
or immortalized cell lines can be created, e.g., by induction of
oncogenes or by loss of tumor suppressor genes.
As used herein, "heparan sulfate" is a member of the
glycosaminoglycan family of carbohydrates. Heparan sulfate is very
closely related in structure to heparin, and they both consist of
repeating disaccharide units which are variably sulfated. The most
common disaccharide unit in heparan sulfate consists of a
glucuronic linked to N-acetyl glucosamine, which typically makes up
approx. 50% of the total disaccharide units.
As used herein, "heparin" is a member of the glycosaminoglycan
family of carbohydrates. Heparin is very closely related in
structure to heparan sulfate, and they both consist of repeating
disaccharide units which are variably sulfated. In heparin, the
most common disaccharide unit consists of a sulfated iduronic acid
linked to a sulfated glucopyranosyl. To differentiate heparin from
heparan sulfate, it has been suggested that in order to qualify a
GAG as heparin, the content of N-sulfate groups should largely
exceed that of N-acetyl groups and the concentration of O-sulfate
groups should exceed those of N-sulfate (Gallagher et al. 1985,
Biochem. J. 230: 665-674).
As used herein, "industrial scale" or large-scale for the
manufacturing of Vaccinia virus or recombinant Vaccinia virus-based
vaccines comprises methods capable of providing a minimum of 50,000
doses of 1.0.times.10.sup.8 virus particles (total minimum
5.0.times.10.sup.12 virus particles) per batch (production run).
Preferably, more than 100,000 doses of 1.0.times.10.sup.8 virus
particles (total minimum 1.0.times.10.sup.13 virus particles) per
batch (production run) are provided.
As used herein, "lab-scale" comprises virus preparation methods of
providing less than 5,000 doses of 1.0.times.10.sup.8 virus
particles (total less than 5.0.times.10.sup.11 virus particles) per
batch (production run).
As used herein, "pilot-scale" comprises virus preparation methods
of providing more than 5,000 doses of 1.0.times.10.sup.8 virus
particles (total more than 5.0.times.10.sup.11 virus particles),
but less than 50,000 doses of 1.0.times.10.sup.8 virus particles
(total minimum 5.0.times.10.sup.12 virus particles) per batch
(production run).
As used herein, "Primary cell culture", refers to the stage where
the cells have been isolated from the relevant tissue (e.g. from
specific pathogen free (SPF) hens eggs), but before the first
sub-culture. This means that the cells have not been grown or
divided any further from the original origin.
As used herein, "Purity" of the Vaccinia virus preparation or
vaccine is investigated in relation to the content of the
impurities DNA, protein, Benzonase, and gentamicin. The purity is
expressed as specific impurity, which is the amount of each
impurity per dose (e.g. ng DNA/dose).
As used herein, "purification" of a Vaccinia virus preparation
refers to the removal or measurable reduction in the level of some
contaminant in a Vaccinia virus preparation.
As used herein, "Recombinant Vaccinia virus" is a virus, where a
piece of foreign genetic material (from e.g. HIV virus) has been
inserted into the viral genome. Thereby, both the Vaccinia virus
genes and any inserted genes will be expressed during infection of
the Vaccinia virus in the host cell.
As used herein, "Stability" means a measure of how the quality of
the virus preparation (Bulk Drug Substance (BDS) or Final Drug
Product (FDP)) varies with time under the influence of a variety of
environmental factors such as temperature, humidity and lights, and
establishes a retest period for the BDS or a shelf-life for the FDP
at recommended storage conditions (Guidance for industry Q1A
(R2).
As used herein, a "Virus preparation" is a suspension containing
virus. The suspension could be from any of the following steps in a
manufacturing process: after virus growth, after virus harvest,
after virus purification (typically the BDS), after formulation, or
the final vaccine (FDP).
As used herein "vaccinia virus forms" refer to the three different
types of virions produced by infected target cells: Mature virions
(MV), wrapped virions (WV), and extra-cellular virions (EV) (Moss,
B. 2006, Virology, 344:48-54). The EV form comprises the two forms
previously known as cell-associated enveloped virus (CEV), and
extra-cellular enveloped virus (EEV) (Smith, G. L. 2002, J. Gen.
Virol. 83: 2915-2931).
The MV and EV forms are morphologically different since the EV form
contains an additional lipoprotein envelope. Furthermore, these two
forms contain different surface proteins, which are involved in the
infection of the target cells by interaction with surface molecules
on the target cell, such as glycosaminglycans (GAGs) (Carter, G. C.
et al. 2005, J. Gen. Virol. 86: 12791290). The invention involves
use of the purification of all forms of Vaccinia Virus.
The different forms of Vaccinia virions contain different surface
proteins, which are involved in the infection of the target cells
by interaction with surface molecules on the target cell, such as
glycosaminglycans (GAGs) (Carter, G. C. et al. 2005, J. Gen. Virol.
86: 1279-1290). These surface proteins will as mentioned supra be
referred to as receptors. On the MV form, a surface protein named
p14 or A27L (the latter term will be used in this application) is
involved in the initial attachment of the virions to the target
cell. A27L binds to GAG structures on the target cell prior to
entry into the cell (Chung C. et al. 1998, J. Virol. 72:
1577-1585), (Hsiao J. C. et al. 1998 J. Virol. 72: 8374-8379),
(Vazquez M. et al. 1999, J. Virol. 73: 9098-9109) (Carter G. C. et
al. 2005, J. Gen. Virol. 86: 1279-1290). The natural ligand for
A27L is presumed to be the GAG known as heparan sulfate (HS).
Heparan Sulfate belongs to a group of molecules known as
glycosaminglycans (GAGs). GAGs are found ubiquitously on cell
surfaces. (Taylor and Drickamer 2006, Introduction to Glycobiology,
2.sup.nd edition, Oxford University Press). GAGs are negatively
charged molecules containing sulfate groups. The A27L protein is
located on the surface of the virions and is anchored to the
membrane by interaction with the A17L protein (Rodriguez D. et al.
1993, J. Virol. 67: 3435-3440) (Vazquez M. et al. 1998, J. Virol.
72: 10126-10137). Therefore, the interaction between A27L and Al17L
can be kept intact during isolation in order to retain full
biological activity of the virions. The specific nature of the
protein-protein interaction between A17L and A27L has not been
fully elucidated, but it has been suggested that a presumed
"Leucine-zipper" region in the A27L is involved in the interaction
with A17L (Vazquez M. et al. 19981, J. Virol. 72: 10126-10137).
The invention encompasses the use of the affinity interaction
between the A27L surface protein on the MV form and
glucosaminglycans, in particular Heparan Sulfate, for purification
of the MV form of Vaccinia Virus.
The term "ligand", thus, refers both to a receptor on a target cell
and to the specific binding structure attached to a solid-phase
matrix used for purification of Vaccinia.
The same principle as described above can be applied to
interactions between other target cell surface structures and other
Vaccinia surface proteins of the MV form participating in the
Vaccinia virus' recognition of, attachment to, entry into and/or
fusion with the target cell. The entire A27L protein, or fragments
thereof containing the binding region for the GAG ligand can be
used as agents to elute Vaccinia viruses-GAG complexes from a
solid-phase column of the invention. Fragments can be readily
generated by routine molecular techniques and screened for their
ability to dissociate Vaccinia viruses-GAG complexes using routine
techniques known in the art, such as by measuring eluted,
biologically active virus.
The presumed native GAG-ligand for the MV form of Vaccinia is
Heparan Sulfate (HS) and can be one of the suitable ligands. The
invention also comprises use of "non-native" ligands for
purification of Vaccinia virus. Such non-native ligands are
compounds with a high degree of structural and/or conformational
similarity to native ligands. As an example, Heparin, which is a
close analogue to the native ligand for A27L, HS, can be used for
affinity-purification of MV form by interaction with the A27L
surface protein, see further below. Heparin has been shown to
partially inhibit the binding between target cells and Vaccinia
virus and can therefore also be used for affinity purification of
the MV form of Vaccinia. Other GAG-ligands and GAG-like ligands can
also be used.
In one embodiment of the invention, Heparan Sulfate, used for
affinity purification of the MV form of Vaccinia, binds A27L on
biologically active Vaccinia viruses, but does not bind inactive
Vaccinia viruses or Vaccinia virus fragments.
The purification of Vaccinia virus using HIC allows for a large
decrease in the level of cellular DNA contamination of the viral
preparation. Thus, a ether, poly-propylene glycol (PPG), phenyl,
butyl or hexyl ligand can be employed.
The ligand makes possible the elution of the bound Vaccinia virus
under such mild conditions that the Vaccinia virus fully retain
their biologically activity. This means that virus is infectious,
for example in CEF cells. The infectivity of the Vaccinia virus can
be preserved during purification such that at least 10%, 20%, 30%,
40%, 50%, 60%, 70%, 80%, or 90% of the initial TCID.sub.50 is
retained during purification. Preferably, at least 30% of the
initial TCID.sub.50 is retained during purification. The
purification can further comprise a step of binding to a
pseudo-affinity (PA) matrix. As used herein, a "pseudo-affinity
(PA) matrix" is a solid-phase matrix with an attached
pseudo-affinity (PA) ligand. As used herein, a "pseudo-affinity
(PA) ligand" is a GAG or GAG-like ligand that binds to Vaccinia
virus virions.
The binding and elution characteristics for the GAG-ligand
substituted matrix depend not only on the individual
characteristics of the matrix and ligand, but also on the interplay
between the two.
By modifying, e.g., the ligand density or by attaching, e.g.
binding or coupling of, the ligand to the matrix by "arms" or
"spacers" of different length and chemical characteristics
(hydrophobicity, hydrophilicity) the binding strength between the
target ligand structure and Vaccinia virus can be altered, which
can be used to enhance the capture or ease the elution.
To enhance the purification method, the matrix in the form of a
chromatography gel or membrane to be used for the purification
preferably: Has a high pore size (to make as many ligands as
possible accessible to the Vaccinia virus) Has a rigid structure to
allow for fast flow rates Is available in a form permitting direct
or indirect attachment, e.g. by binding or coupling, of ligands Is
applicable for sterilization in place or available as a
pre-sterilized unit, e.g. by using radiation.
In one embodiment, the solid phase matrix is a gel or membrane with
a pore size of 0.25 .mu.m, preferably of more than 0.25 .mu.m, more
preferably of 1.0-3.0 .mu.m demonstrating a linear flow rate under
actual purification conditions of 10 cm/min, preferably 20 cm/min.
The pore size of the matrix can be 0.25-0.5 .mu.m, 0.5-0.75 .mu.m,
0.75-1.0 .mu.m, 1.0-2.0 .mu.m, 2.0-3.0 .mu.m, or greater than 3.0
.mu.m.
In one embodiment, with the solid phase matrix containing a heparan
sulfate as an immobilized ligand, the virus harvest from the
upstream virus growth process is loaded in a crude (unpurified)
form with a flow rate of 10 cm/min, preferably 20 cm/min at a virus
concentration of 10.sup.6 virions per mL in pilot scale and
10.sup.7 virions per mL in industrial scale.
In one embodiment, there are three steps in the purification
process of the invention, which are common for most affinity
chromatography processes:
1) Loading of Vaccinia virus or Vaccinia recombinant virus onto the
solid phase;
2) Washing of the solid phase to remove contaminants; and
3) Elution of the Vaccinia virus or recombinant virus to be
isolated.
Step 1. Loading of Vaccinia Virus or Recombinant Virus onto a
Solid-Phase Matrix
Loading the solid phase with a ligand can be performed by a batch-,
column- or membrane approach.
The membrane approach can have some benefits, specifically for
large bio-molecules, in particular for large viruses like Vaccinia
viruses: For example, large pore sizes and the availability of the
ligand on the surface of the membrane allow high binding capacities
of even large viral particles. The membrane approach is, thus, a
preferred embodiment of the present invention.
In all embodiments mentioned above, the Vaccinia virus or
recombinant virus to be isolated is present in a liquid phase. When
the Vaccinia virus or recombinant virus gets close to the ligand,
the Vaccinia virus will bind specifically to or be "captured by"
the ligand, thereby the Vaccinia virus or recombinant Vaccinia
virus can be temporarily immobilized on the solid phase, while the
contaminants will remain in the liquid phase.
By appropriate selection of the ligand type, ligand density and
ligand steric configuration, the binding parameters of Vaccinia
virus to the solid phase can be altered, thereby providing means
for optimization of the purification parameters.
In one embodiment, the virus is bound to the ligand in ammonium
sulphate, for example, at 0.3M, 0.45M, 0.6M, 0.85M, 1.0M, 1.25M,
1.5M, 1.7M, 1.85M, or 2.0M.
In various embodiments, the virus is bound to the ligand in citric
acid, for example at 100 mM, or with K.sub.2HPO.sub.4, for example
at 50 mM at pH7.4. In preferred embodiments, the virus is bound in
ammonium sulphate containing 50 mM K.sub.2HPO.sub.4 at pH7.4.
Step 2. Washing of the Solid Phase to Remove Contaminants
When the binding of the biologically active Vaccinia viruses or
recombinant viruses to the ligand has proceeded sufficiently, the
host cell contaminants (in particular host cell DNA and proteins)
that remain in the liquid phase can be removed by washing the solid
phase, to which the Vaccinia virus is bound, with an appropriate
washing medium.
In one embodiment, the solid phase is washed with ammonium
sulphate, for example, at 0.3M, 0.45M, 0.6M, 0.85M, 1.0M, 1.25M,
1.5M, 1.7M, 1.85M, or 2.0M.
In various embodiments, the solid phase is washed with citric acid,
for example at 100 mM, or with K.sub.2HPO.sub.4, for example at 50
mM at pH7.4.
Step 3. Eluting the Vaccinia Virus or Recombinant Virus by Specific
or Non-Specific Agents
The biologically active Vaccinia viruses or recombinant viruses can
be eluted. The elution of the captured Vaccinia virus can be
performed, for example, by:
Agents specifically disrupting the specific interaction between the
ligand and a L surface protein on the Vaccinia virus (to be called
specific agents), or by:
Agents non-specifically disrupting the electrostatic interaction
between the ligand and the surface protein (to be called
non-specific agents).
In one embodiment, the agent is ammonium sulphate, for example, at
0.3M, 0.45M, 0.6M, 0.85M, 1.0M, 1.25M, 1.5M, 1.7M, 1.85M, or
2.0M.
In various embodiments, the agent is citric acid, for example at
100 mM, or K.sub.2HPO.sub.4, for example at 50 mM at pH7.4.
According to further embodiments of the present invention, the
Vaccinia virus is eluted with GAG or a GAG-like ligand or part
thereof, with the GAG-binding domain of A27L or part thereof,
and/or with an 0-glycoside-binding cleaving enzyme.
In another embodiment, the agent is sodium chloride, more
preferably, an increasing NaCl concentration gradient ranging from
0.15 M to 2.0 M.
Pre-Treatment
Prior to loading on the solid phase, a pre-treatment of the virus
suspension can be performed, specifically in order to remove
contaminants from the Vaccinia virus in the liquid-phase
culture.
Pre-treatment can be one or more of the following steps either
alone or in combination:
1) Homogenization of the Host Cells Ultrasound treatment
Freeze/thaw Hypo-osmotic lysis High-pressure treatment
2) Removal of Cell Debris Centrifugation Filtration
3) Removal/Reduction of Host Cell DNA Benzonase treatment Cationic
exchange Selective precipitation by cationic detergents
According to a further embodiment of the invention, the pH value of
the viral suspension is decreased just prior to loading in order to
improve the binding of the virus particle to the ligand. The pH
value of the viral suspension can be decreased from appr. pH
7.0-8.0 to 4.0-6.9, in particular to pH 4.0, 4.2, 4.4, 4.5, 4.6,
4.8, 5.0, 5.2, 5.4, 5.5, 5.6, 5.8, 6.0, 6.2, 6.4, 6.5, 6.6, 6.8,
6.9. Preferably, the pH value is decreased from pH 7.0-8.0 to pH
5.8. Subsequently, just after loading and before elution, the pH
value is again increased to pH 7.0-8.0, in particular to pH 7.0,
7.2, 7.4, 7.5, 7.6, 7.8, 8.0, preferably to pH 7.7, in order to
improve the stability of the viral particles.
Post-Treatment
Depending on the agent used for elution of the Vaccinia virus or
recombinant virus, post-treatment can be performed to enhance the
purity of the virus preparation. The post-treatment could be
ultra/diafiltration for further removal of impurities and/or
specific or non-specific agents used for elution. To obtain an
efficient purification of the virus, it is also preferred to
combine the purification according to the invention with one or
more further purification steps, e.g., by ion-exchange(s).
Ion-exchange(s) can, then, also be performed as post-treatment
step(s).
In order to prevent aggregation of the purified virus suspension
and, thus, to, inter alia, improve the detection of infectious
particles, in particular by the TCID.sub.50 method, it can also be
suitable to increase the pH value after elution of the virus, in
particular to a pH value of up to 9 or more, in particular to pH
7.5, 7.6, 7.8, 8.0, 8.2, 8.4, 8.5, 8.6, 8.8, 9.0, 9.2, 9.4, 9.5,
9.6, 9.8, 10.0, 10.2, 10.4, 10.5. Preferably, the pH value is
increased from, in particular, pH 7.0, 7.2, 7.4, 7.5, 7.6, 7.8,
8.0, preferably pH 7.7 to pH 9.0.
Preferably, the amount of host-cell DNA in a VV dose of
1.times.10.sup.8 TCID.sub.50 is 10-20 .mu.g, 1-10 .mu.g, 100 ng-1
.mu.g, 10-100 ng, or 1-10 ng. In various embodiments, the amount of
host-cell DNA is less than 100 ng, 50 ng, 20 ng, 10 ng, 5 ng, or 1
ng per ml or less than 100 ng, 50 ng, 20 ng, 10 ng, 5 ng, or 1 ng.
The amount of dsDNA in a VV sample can be reduced by the
purification method to less than 40%, 20%, 10%, 5%, 2.5, 1%, 0.5%,
0.25%, 0.1%, 0.05%, 0.02% or 0.01% of input.
In various embodiments, the amount of protein in the purified VV is
less than 250 .mu.g/ml, 100 .mu.g/ml, 50 .mu.g/ml, 20 .mu.g/ml, 10
.mu.g/ml, or 5 .mu.g/ml. In various embodiments, the amount of
protein in the purified VV is less than 250 .mu.g/1.times.10.sup.8
TCID.sub.50, 100 .mu.g/1.times.10.sup.8 TCID.sub.50, 50
.mu.g/1.times.10.sup.8 TCID.sub.50, 20 .mu.g/1.times.10.sup.8
TCID.sub.50, 10 .mu.g/1.times.10.sup.8 TCID.sub.50, or 5
.mu.g/1.times.10.sup.8 TCID.sub.50. The amount of contaminating
protein is preferably less than 40%, 20%, 10%, 5%, 2.5, 1%, 0.5%,
0.25%, 0.1%, 0.05%, 0.02% or 0.01% of input.
The practice of the invention employs techniques in molecular
biology, protein analysis, and microbiology, which are within the
skilled practitioner of the art. Such techniques are explained
fully in, for example, Ausubel et al. 1995, eds, Current Protocols
in Molecular Biology, John Wiley & Sons, New York.
Modifications and variations of this invention will be apparent to
those skilled in the art. The specific embodiments described herein
are offered by the way of example only, and the invention is not to
be construed as limited thereby. Additional aspects and advantages
of the invention will be set forth in part in the description which
follows, and in part will be obvious from the description, or may
be learned by practice of the invention.
In one embodiment, the invention provides a more time-effective and
cost-effective process for purification of Vaccinia viruses and
recombinant-modified Vaccinia viruses in higher yield, comprising
one or more of the following steps:
a. loading a solid-phase matrix with a liquid-phase virus
preparation, wherein the solid-phase matrix comprises a ligand
appropriate for interacting with the virus, e.g. by reversibly
binding the virus
b. washing of the matrix, and
c. eluting the virus.
In a preferred embodiment, the method comprises the following
steps:
a. Loading a column, membrane, filter or similar solid-phase matrix
comprising one or more appropriate virus-binding ligands with a
liquid-phase virus preparation,
b. Washing of the matrix with an appropriate solvent to remove
contaminants, and
c. Eluting the Vaccinia virus with an appropriate solvent to
achieve a highly pure, biologically active, stable virus
preparation.
In a further preferred embodiment, the method comprises the
following steps:
a. Loading a column, membrane, filter or similar solid-phase matrix
comprising one or more appropriate HIC ligands with a liquid-phase
virus preparation
b. Washing of the matrix with an appropriate solvent to remove
contaminants, and
c. Eluting the Vaccinia virus with citric acid, for example at 100
mM, or K.sub.2HPO.sub.4, for example at 50 mM at pH7.4, to achieve
a highly pure, biologically active, stable virus preparation.
In one particularly preferred embodiment, the method is used for
the purification of biologically active Vaccinia virus and
comprises the following steps:
a. Loading a column, membrane, filter or similar solid-phase HIC
matrix substituted with a phenyl or PPG group with a Vaccinia virus
preparation dissolved in a neutral buffer (pH 6.5 to 8.5,
preferably >=pH 7.5) in ammonium sulphate, preferably at
1.5-1.7M,
b. Washing of the matrix with a sufficient amount of the loading
buffer to ensure complete elution of all non-binding Vaccinia virus
particles and non-binding contaminants, and
c. Eluting the Vaccinia virus with citric acid, for example at 100
mM, or K.sub.2HPO.sub.4, for example at 50 mM at pH7.4 to obtain
the biologically active Vaccinia virus particles.
In another particularly preferred embodiment, the method is used
for the purification of biologically active Vaccinia virus and
comprises the following steps:
a. Loading a column, membrane, filter or similar solid-phase matrix
substituted with a Heparin (HP) with a Vaccinia virus preparation
dissolved in a neutral buffer (pH 6.5 to 8.5, preferably >=pH
7.5) with a physiological salt concentration (approximately 150 mM
NaCl). An appropriate buffer is Phosphate Buffered Saline (PBS),
e.g. 0.01 to 0.1 M phosphate, 0.15 M NaCl, pH 7.5. Other
appropriate buffers are Tris-NaCl, e.g. 0.01 to 0.1 M Tris, 0.15 M,
or citric acid, at 100 mM, or K.sub.2HPO.sub.4 at 50 mM at
pH7.4.
b. Washing of the matrix with a sufficient amount of the loading
buffer to ensure complete elution of all non-binding Vaccinia virus
particles and non-binding contaminants, for example, as measured by
the return of the 280 nm absorbance signal to the pre-loading
baseline, and
c. Eluting the Vaccinia virus with 1.5-1.7M ammonium sulphate
containing 50 mM K.sub.2HPO.sub.4 at pH7.4.
In another particularly preferred embodiment, the method is used
for the purification of biologically active Vaccinia virus and
comprises the following steps:
a. Loading a column, membrane, filter or similar solid-phase
sulphated cellulose matrix with a Vaccinia virus preparation
dissolved in a neutral buffer (pH 6.5 to 8.5, preferably >=pH
7.5) with a physiological salt concentration (approximately 150 mM
NaCl). An appropriate buffer is Phosphate Buffered Saline (PBS),
e.g. 0.01 to 0.1 M phosphate, 0.15 M NaCl, pH 7.5. Other
appropriate buffers are Tris-NaCl, e.g. 0.01 to 0.1 M Tris, 0.15 M,
or citric acid, at 100 mM, or K.sub.2HPO.sub.4 at 50 mM at
pH7.4.
b. Washing of the matrix with a sufficient amount of the loading
buffer to ensure complete elution of all non-binding Vaccinia virus
particles and non-binding contaminants, for example, as measured by
the return of the 280 nm absorbance signal to the pre-loading
baseline, and
c. Eluting the Vaccinia virus with 1.5-1.7M ammonium sulphate
containing 50 mM K.sub.2HPO.sub.4 at pH7.4.
In another particularly preferred embodiment, the method is used
for the purification of biologically active Vaccinia virus and
comprises the following steps:
a. Loading a column, membrane, filter or similar solid-phase matrix
substituted with a Heparin (HP) with a Vaccinia virus preparation
dissolved in a neutral buffer (pH 6.5 to 8.5, preferably >=pH
7.5) with a physiological salt concentration (approximately 150 mM
NaCl). An appropriate buffer is Phosphate Buffered Saline (PBS),
e.g. 0.01 to 0.1 M phosphate, 0.15 M NaCl, pH 7.5. Other
appropriate buffers are Tris-NaCl, e.g. 0.01 to 0.1 M Tris, 0.15 M,
or citric acid, at 100 mM, or K.sub.2HPO.sub.4 at 50 mM at
pH7.4.
b. Washing of the matrix with a sufficient amount of the loading
buffer to ensure complete elution of all non-binding Vaccinia virus
particles and non-binding contaminants, for example, as measured by
the return of the 280 nm absorbance signal to the pre-loading
baseline,
c. Eluting the Vaccinia virus with 1.5-1.7M ammonium sulphate
containing 50 mM K.sub.2HPO.sub.4 at pH7.4,
d. Loading a column, membrane, filter or similar solid-phase HIC
matrix with the eluted Vaccinia virus preparation,
e. Washing of the matrix with a sufficient amount of the loading
buffer to ensure complete elution of all non-binding Vaccinia virus
particles and non-binding contaminants, and
f. Eluting the Vaccinia virus with citric acid, for example at 100
mM, or K.sub.2HPO.sub.4, for example at 50 mM at pH7.4 to obtain
the biologically active Vaccinia virus particles.
In another particularly preferred embodiment, the method is used
for the purification of biologically active Vaccinia virus and
comprises the following steps:
a. Loading a column, membrane, filter or similar solid-phase
sulphated cellulose matrix with a Vaccinia virus preparation
dissolved in a neutral buffer (pH 6.5 to 8.5, preferably >=pH
7.5) with a physiological salt concentration (approximately 150 mM
NaCl). An appropriate buffer is Phosphate Buffered Saline (PBS),
e.g. 0.01 to 0.1 M phosphate, 0.15 M NaCl, pH 7.5. Other
appropriate buffers are Tris-NaCl, e.g. 0.01 to 0.1 M Tris, 0.15 M,
or citric acid, at 100 mM, or K.sub.2HPO.sub.4 at 50 mM at
pH7.4.
b. Washing of the matrix with a sufficient amount of the loading
buffer to ensure complete elution of all non-binding Vaccinia virus
particles and non-binding contaminants, for example, as measured by
the return of the 280 nm absorbance signal to the pre-loading
baseline, and
c. Eluting the Vaccinia virus with 1.5-1.7M ammonium sulphate
containing 50 mM K.sub.2HPO.sub.4 at pH7.4,
d. Loading a column, membrane, filter or similar solid-phase HIC
matrix with the eluted Vaccinia virus preparation,
e. Washing of the matrix with a sufficient amount of the loading
buffer to ensure complete elution of all non-binding Vaccinia virus
particles and non-binding contaminants, and
f. Eluting the Vaccinia virus with citric acid, for example at 100
mM, or K.sub.2HPO.sub.4, for example at 50 mM at pH7.4 to obtain
the biologically active Vaccinia virus particles.
EXAMPLE 1
Production of Modified Vaccinia Ankara Virus Particles
MVA-BN.RTM. virus particles were produced by Bavarian Nordic A/S
(Denmark) in primary cultures of CEF cells under Good Manufacturing
Practice conditions (Vollmar et al., 2006). Different batches of
the starting material were provided after homogenization and
clarification as a liquid frozen product, stored in aliquots at
-80.degree. C. The initial TCID.sub.50 values of the samples were
calculated.
EXAMPLE 2
Total Protein Assay
Total protein concentrations were determined in triplicates by the
Pierce.RTM. BCA protein assay reagent kit (Cat.#23225, Pierce
Biotechnology, USA) as recently described (Wolff et al. 2009). The
assay was calibrated against albumin standards (BSA) (Cat.#23209,
Thermo Fisher Scientific Inc., USA) within the validated working
range of 25 to 250 .mu.g/ml (limit of detection: 8.3 .mu.g/ml;
limit of quantification: 25 .mu.g/ml).
EXAMPLE 3
Quantification of MVA-BN.RTM. Virus Particles
Total MVA-BN.RTM. virus particles were quantified in triplicates by
a sandwich ELISA as described previously (Wolff et al. 2009).
Infectious MVA-BN.RTM. virus particles were determined by the 50%
tissue culture infective dose assay (TCID.sub.50) in Vero cells
(ECACC; Cat.#88020401, UK; 2.0.times.10.sup.5 cells/well) as a
variation of the procedure described by Jordan et al. (Jordan et
al. 2009). Briefly, Vero cells were maintained in high glucose (4.5
g/l) DMEM-medium (Cat.# E15-009, PAA Laboratories GmbH, Colbe,
Germany) containing 4 mM glutamin (Cat.# G-3126-250G Sigma-Aldrich,
Munchen, Germany), 0.1% gentamycin (Cat.#15710080, Invitrogen,
Karlsruhe, Germany) and 10% FBS (Cat.#3302-P280703, PAN-Biotech
GmbH, Aidenbach, Germany) at 37.degree. C. and 5% CO.sub.2. Serial
10-fold dilutions of the virus containing samples were added to
Vero monolayers. After incubation (48 h) the cells were fixed with
a 1:2 acetone (Cat.# CP40.3, Carl Roth, Karlsuhe, Germany):
methanol (Cat.#106018, Merck, Darmstadt, Germany) mixture and
incubated with a polyclonal rabbit anit-vaccinia virus antibody
(Cat.#220100717, Quartett Immunodiagnostika & Biotechnologie
GmbH, Berlin, Germany) at 1:1000 dilution in PBS containing 1% FBS.
Subsequently, the wells were washed with PBS and incubated with the
secondary antibody (anit-rabbit IgG, peroxidase conjugated, Cat.#
W401B, Promega GmbH, Mannheim, Germany) in PBS containing 1% FBS.
The peroxidase enzyme of the secondary antibody catalyses a color
reaction upon incubation with ACE substrate solution (0.3 mg/ml
3-amino-9-ethyl-carbozole (Cat.# A5754-10G, Sigma-Aldrich, Munchen,
Germany) in 0.1 M Na-acetate buffer pH 5.0 containing 0.015%
H.sub.2O.sub.2 (Cat.#1.07209.0250, Merck, Darmstadt, Germany).
Infected forci were identified under the light microscope and the
TCID.sub.50 is calculated from the maximum dilution of MVA-BN.RTM.
suspension that yields positive dye reaction. All titrations were
performed in parallel replicates.
EXAMPLE 4
DNA-Quantification Assays
The dsDNA measurements in a validated working range from 4 to 1000
ng/ml were done as described by Opitz et al. (Opitz et al. 2007)
using the Quant-iT.TM. PicoGreen.RTM. dsDNA reagent from Molecular
Probes, Inc. (Cat.# P7581, Eugene, Oreg., USA). Calibration was
done against lambda DNA (Cat.# D1501, Promega Corporation, Madison,
Wis., USA) within the validated working range of 4 to 1000 ng/ml
(weighted regression; limit of detection: 0.66 ng/ml; limit of
quantification: 2.36 ng/ml) using 100 mM citric acid buffer pH 7.2
for dilutions.
Total DNA measurements in a range of 6 to 400 pg/ml were done by
the total DNA Threshold assay method after protease treatment and
DNA extraction.
EXAMPLE 5
Protease Treatment
Samples were dialysed (5000 kDa MWCO; Cat.#131192, Sectrum Europe
B.V., Breda, Netherlands) against 50 mM phosphate buffered saline
containing 1 mM EDTA and 0.05% NaN.sub.3, pH 7.0 and appropriately
diluted in the Zero Calibrator solution (50 mM PBS, 1 mM EDTA,
0.05% NaN.sub.3, pH 7.0; Cat.# R 8004, MDS Analytical Technologies,
Ismaningen, Germany) containing 0.01 mg/ml SDS (Cat.# L 6026,
Sigma-Aldrich, Munchen, Germany) and 0.01 mg/ml Proteinase K (Cat.#
P8102S, New England Biolabs GmbH, Frankfurt, Germany) and incubated
over night at 56.degree. C.
EXAMPLE 6
DNA Extraction
The DNA was extracted after protease treatment using a DNA
extractor kit (Cat.#295-58501, Wako Chemicals GmbH, Neuss, Germany)
according to the manufactures instructions.
EXAMPLE 7
DNA Quantification
DNA Quantification was done by the Threshold Total DNA Assay Kit
(Cat.# R 9009, MDS Analytical Technologies, Ismaning, Germany) and
workstation (MDS Analytical Technologies, Ismaning, Germany) as
described in the following. After extraction, samples were adjusted
to 500 .mu.l with zero calibrator solution and heat denatured at
105.degree. C. for 15 min. 1000 .mu.l of a mixture containing
biotin-conjugated, high affinity, single-stranded DNA binding
protein, streptavidine and urease-conjugated monoclonal antibody
against single-stranded DNA (ssDNA) were added to each sample or
standard and incubated for 1 hour at 37.degree. C. The reaction
mixtures were transferred to individual wells in the manifold of
the Threshold workstation. Mixtures were filtered through the
biotin-coated nitrocellulose membrane adsorber under controlled
vacuum. Subsequently, the wells were washed (wash solution,
phosphate buffered saline, pH 6.5 containing 0.05% NaN.sub.3 and
0.05% Tween 20) and the filtration was continued under high vacuum
until all wells were dry. Then the dipstick membrane adsorbers were
transferred to the Threshold reader which contained the substrate
urea (600 .mu.l of 5 M urea containing 0.05% NaN.sub.3 and 30 .mu.l
wash solution) and the light-addressable potentiometric sensor.
Captured urease in the DNA-protein complexes hydrolyses urea which
results in detectable pH changes in the substrate solution. All
samples were measured in triplicates. The assay was calibrated
against calf thymus DNA and all samples were analyzed additionally
by spiking them with (50 pg) calf thymus DNA in order to estimate
spike recoveries according to the manufacturer's recommendations.
All the controls were within the range indicated on the certificate
of analysis from the supplier.
EXAMPLE 8
Chromatography Materials
Pseudo-Affinity Membrane Adsorbers--
Heparin-MA was a research product of Sartorius Stedim Biotech GmbH,
Gottingen, Germany. It was based on reinforced stabilized cellulose
with a pore size >3 .mu.m and adsorption area of 3.times.75
cm.sup.2 by 3.times.15 layers. The housing material was
polypropylene. Sulfated cellulose MA (SC-MA) with a diameter of 25
mm (pore size >3 .mu.m, Sartorius Stedim Biotech GmbH,
Gottingen, Germany) were prepared as described previously (Opitz et
al. 2009), except that the membrane discs were incubated for 12
hours at 35.degree. C., 40.degree. C. and 45.degree. C. The
adsorption area was 75 cm.sup.2, and 15 membrane discs were stacked
in a stainless steel membrane holder (Cat.#1980-002, GE Healthcare,
Munchen, Germany). Membrane adsorbers prepared at 40.degree. C.
have been applied for the majority of experiments, other membranes
were used to optimize the sulfation degree in terms of dynamic
binding capacity and purity. Sulfate ion content of blank and
modified sulfated cellulose MA was estimated by the Schoniger
decomposition method followed by ion exchange chromatography
(Currenta GmbH & Co. OHG, Leverkusen, Germany)
Hydrophobic Interaction Chromatography Matrices--
Experiments were done with 1 ml columns of the ToyoScreen HIC Mix
Pack (Cat.#21398, Tosoh Bioscience GmbH, Stuttgart, Germany). The
screened resins comprised ToyoScreen.RTM. Hexyl-650C,
ToyoScreen.RTM. Butyl-600M, ToyoScreen.RTM. Phenyl-650M,
ToyoScreen.RTM. PPG-600M, ToyoScreen.RTM. Ether 650M.
EXAMPLE 9
Adsorption Chromatography
Chromatography was performed using an Akta Explorer system (GE
Healthcare, Munchen, Germany) at a flow rate of 1.0 ml/min and
monitored by UV (280 nm) and light scattering (90.degree., Dawn
EOS, Wyatt Technology Europe GmbH, Dernbach, Deutschland)
detection.
Dynamic binding capacity of the HIC-chromatography media was
determined loading the clarified MVA-BN.RTM. virus sample
(1.85.times.10.sup.8 TCID.sub.50/ml) in adsorption buffer (1.7 M
(NH.sub.4).sub.2SO.sub.4+50 mM K.sub.2HPO.sub.4, pH 7.4; HIC (1.7))
onto equilibrated (HIC (1.7) adsorption buffer) 1 ml columns of the
HIC-columns. The breakthrough was monitored via light scattering
detector and the virus particles were eluted with 50 mM
K.sub.2HPO.sub.4, pH 7.4.
Dynamic binding capacities of the pseudo-affinity MA (SC-MA and
heparin-MA) were determined loading the clarified MVA-BN.RTM. virus
sample (1.85.times.10.sup.8 and 4.65.times.10.sup.7 TCID.sub.50/ml)
in SC-MA adsorption buffer (100 mM citric acid, pH 7.4) at a flow
rate of 1 ml/min onto equilibrated (SC-MA adsorption buffer) 75
cm.sup.2 SC-MA and heparin-MA. The breakthrough was monitored via
light scattering detector and the virus particles were eluted with
100 mM citric acid containing 2 M NaCl, pH 7.4. The eluted product
fraction was dialysed against adsorption buffer with a MWCO of 5000
kDa (Cat.#131192, Spectrum Europe B.V., Breda, Netherlands) and the
virus and DNA content was quantified as described above.
Characterization of the HIC-materials was done with 4 ml of the
clarified MVA-BN.RTM. virus sample (4.65.times.10.sup.7
TCID.sub.50/ml) in HIC (1.7) and HIC (1.5; 1.5 M
(NH.sub.4).sub.2SO.sub.4+50 mM K.sub.2HPO.sub.4, pH 7.4) adsorption
buffer. Prior to sample loading the chromatography material was
equilibrated with the respective HIC adsorption buffers. After a
brief washing (respective HIC adsorption buffer) the bound virus
particles were eluted with elution buffer (50 mM K.sub.2HPO.sub.4,
pH 7.4). Resulting fractions were pooled and analyzed for virus and
contaminant compositions. Chromatographic materials were
regenerated after each run with 10 column volumes of 0.5 M NaOH and
0.1 M HCl. All experiments were performed in triplicates.
Optimization of the Ammonium Sulfate Concentration for the
MVA-BN.RTM. Adsorption onto HIC-Phenyl Resin
The study was done as the characterization of the different
HIC-matrices described above. However, the HIC-adsorption buffer
for the sample loading and column equilibration varied. The tested
adsorption buffers contained 0.45, 0.6, 0.85, 1.0, 1.25, 1.5 and
1.7 M (NH.sub.4).sub.2SO.sub.4 and 50 mM K.sub.2HPO.sub.4, pH
7.4.
Combination of Pseudo-Affinity MA and HIC
The chromatography was performed using the same system and
monitored as described above at a flow rate of 1.0 ml/min. Four ml
of the clarified MVA-BN.RTM. virus sample (4.65.times.10.sup.7
TCID.sub.50/ml) in 100 mM citric acid, pH 7.4 or 50 mM
K.sub.2HPO.sub.4, pH 7.4 have been subjected to an equilibrated
(100 mM citric acid, pH 7.4 or 50 mM K.sub.2HPO.sub.4, pH 7.4)
SC-MA (75 cm.sup.2) or heparin-MA (225 cm.sup.2). The virus was
eluted from the pseudo-affinity MA after a brief washing (100 mM
citric acid, pH 7.4 or 50 mM K.sub.2HPO.sub.4, pH 7.4) in HIC (1.5
and 1.7) adsorption buffer. The pooled eluted fractions were
directly loaded onto an equilibrated (respective HIC-adsorption
buffer) ToyoScreen.RTM. Phenyl-650M or ToyoScreen.RTM. PPG-600M
column. The adsorbed virus particles were desorbed after washing
(respective HIC-adsorption buffer) from the HIC-matrices with 50 mM
K.sub.2HPO.sub.4 pH 7.4 or 100 mM citric acid pH 7.4. Pooled
fractions were stored at -80.degree. C. The virus content and the
amount of total dsDNA and protein were determined from
representative samples as described above. Analytical samples
removed were considered in the overall mass balances.
Optimization of the Pseudo-Affinity Membrane Adsorbers
Table 1 demonstrates the dependence of the cellulose sulfation on
the chemical reaction temperature. Reaction temperatures of 35, 40
and 45.degree. C. resulted in 5.5, 9.3 and 13 weight % sulfation of
the cellulose backbone. The dynamic binding capacity up to 50 ml
(9.3.times.10.sup.9 TCID.sub.50) MVA-BN.RTM. was not affected by
the degree of sulfation. However, the performance in terms of
product adsorption and DNA depletion varied among the tested SC-MA.
The SC-MA modified at the lowest reaction temperature reflects the
modest amount of adsorbed virus particles (66%). In contrast, SC-MA
sulfated at 40.degree. C. and 45.degree. C. yielded a product
recovery of 79% and 80%, respectively. The amount of total DNA in
the product fraction increased with the degree of sulfation. The
relative amount of DNA based on the starting material in the
product was for the SC-MA produced at 35.degree. C., 40.degree. C.
and 45.degree. C. 7.4%, 14% and 17%, respectively. The unmodified
cellulose backbone bound 15% DNA whereas 31% of the MVA-BN.RTM.
virus particles adsorbed to it. Recent studies demonstrated the
encouraging performance of pseudo-affinity MA based on sulfated
cellulose compared to ion exchange MA (Wolff et al. 2009). These
studies were conducted with MA sulfated at a reaction temperature
of 37.degree. C. and suffered from losses (36%; (Wolff et al.
2009)) of virus particles during the adsorption process.
Table 1 indicates that elevated cellulose sulfation lead within the
tested temperature range to improved adsorption of the MVA-BN.RTM.
virus particles. The level of sulfation also seems to affect the
DNA adsorption. Higher sulfated SC-MA resulted in enhanced
adsorption of total DNA (Tab. 1). In contrast un-sulfated (<0.05
wt %) cellulose disks adsorbed 15% of the initial DNA content
compared to 7.4% of the least sulfated (5.5 wt %) SC-MA. This
phenomenon can be explained by different interaction modes between
sulfated and un-sulfated cellulose and DNA-molecules. The
adsorption of DNA to hydrophilic surfaces like cellulose is
commonly known and described in the literature as e.g. the partial
adsorption of nucleic acids to cellulose powder (Halder et al.
2005) and the adsorption of non-circular DNA to a highly porous
cellulose matrix (Deshmukh and Lali 2005). Enlarged DNA adsorption
at an increasing degree of sulfation is unexpected due to the ionic
phosphate groups of nucleic acids. However, previous studies with
CEF cell-derived MVA-BN.RTM. virus particles displayed compared to
anion exchange MA a limited adsorption of dsDNA to weak cation
exchange MA and to the cationic pseudo-affinity MA like sulfated
cellulose and heparin as well as the bead-based sulfated cellulose
resin Cellufine.RTM. sulfate (Wolff et al. 2009). Opitz et al.
demonstrated similarly the adsorption of host cell DNA during the
primary capturing step of MDCK cell-derived influenza virus
particles to strong and weak cation exchange MA (Opitz et al.
2009).
Table 1: Effect of the sulfation degree from sulfated cellulose on
the dynamic binding capacity, purity and overall virus yield.
Relative amounts (mean and standard deviation of triplicates) for
MVA-BN.RTM. (ELISA) and dsDNA (Quant-iT.RTM. PicoGreen.RTM. assay)
content were calculated based on the starting material of the
homogenized and clarified virus broth. The adsorption area of the
SC-MA was 75 cm.sub.2. Equilibration and wash buffer was 100 mM
citric acid, pH 7.4, and the elution buffer 100 mM citric acid+2 M
NaCl, pH 7.4. The product recoveries from the cellulose backbone
(blank) and the sulfated cellulose MA were estimated from 2
chromatographic experiments. The dynamic binding capacity
experiments were done twice.
TABLE-US-00001 TABLE 1 Dynamic Recoveries in Chroma- Sul- Binding
Capacity Product Fraction tography fation Volume Total TCID.sub.50
MVA-BN .RTM. Total Media [wt %] [ml] [TCID.sub.50 ] [%] DNA [%]
Cellulose <0.05 n. d. n. d. 31 .+-. 0.2 15 .+-. 0.4 backbone
SC-MA 5.5 >50 >9.3 .times. 10.sup.9 66 .+-. 3.3 7.4 .+-. 1.5
35.degree. C. SC-MA 9.3 >50 >9.3 .times. 10.sup.9 79 .+-. 2.4
14 .+-. 0.6 40.degree. C. SC-MA 13 >50 >9.3 .times. 10.sup.9
80 .+-. 6.7 17 .+-. 0.5 45.degree. C.
Dynamic Binding Capacities of the Tested HIC-Resins and
Pseudo-Affinity MA
Table 2 shows the dynamic binding capacities of the tested
chromatography materials. The capacity of all tested HIC resins was
greater than 20 ml of the homogenized and clarified harvest
(3.7.times.10.sup.9 TCID.sub.50). After 20 ml the addition of
MVA-BN.RTM. virus sample was stopped, because the dynamic binding
capacity was judged sufficient for the characterization of the HIC
columns. The capacity of the heparin-MA was 6.0 ml corresponding to
1.1.times.10.sup.9 TCID.sub.50, and the capacity of the SC-MA as
already discussed was independent of the degree of sulfation
greater than 50 ml (9.3.times.10.sup.9 TCID.sub.50; Tab. 1). The
high dynamic binding capacity for the SC-MA was verified via
quantification of the viral particles after elution from the SC-MA
and compared with data obtained during the characterization of the
SC-MA. The recovered virus particles based on the loaded sample for
50 ml and 4 ml were 81% and 79%, respectively. The un-adsorbed
virus particles were for the respective experiments 22% and 23%.
Thus, it can be assumed that the virus particles of
9.3.times.10.sup.9 TCID.sub.50 did adsorb to the MA and filtration
effects at a pore size of 3 to 5 .mu.m, if at all, are negligible.
Furthermore, these experiments confirm that non-specific binding to
the chromatography materials at the selected volume for the
characterization studies (4 ml) were insignificant. Loading of the
MVA-BN.RTM. virus sample during the dynamic binding capacity
studies was stopped after 50 ml to conserve sample. Earlier studies
demonstrated the high dynamic binding capacity for Cellufine.RTM.
sulfate, a commercial bead based resin constituted of sulfated
cellulose beads, supporting the observed high capacity of SC-MA
(Wolff et al. 2009).
Table 2: Dynamic binding capacity of the tested chromatography
materials. The adsorption buffer for the hydrophobic interaction
chromatography media (1 ml column) was 1.7 M
(NH.sub.4).sub.2SO.sub.4+50 mM K.sub.2HPO.sub.4, pH 7.4 and for the
pseudo-affinity membrane adsorbers (gray; adsorption area: 75
cm.sup.2) 100 mM citric acid, pH 7.4.
TABLE-US-00002 TABLE 2 ##STR00001##
Screening of HIC Resins
Preliminary studies with NaCl (2 M), an intermediate chaotropic
salt did not lead to sufficient adsorption of virus particles or
nucleic acids (data not shown) to ethyl, phenyl and hexyl ligands.
Hence, the suitability of HIC for the depletion of contaminating
DNA after pseudo-affinity chromatography was evaluated during this
study with a strong antichaotropic salt, ammonium sulfate, with a
series of different hydrophobic ligands. Selection of the most
promising HIC-ligands was conducted in experiments comprising the
following ligands: ether, poly-propylene glycol (PPG), phenyl,
butyl, and hexyl. The outcomes of these experiments are combined in
FIG. 1. The majority of MVA-BN.RTM. virus particles adsorbed to the
tested HIC-resins. For the PPG and phenyl ligand, no virus
particles were detected via ELISA in the flow through fraction
under the applied conditions. In case of the ether, butyl and hexyl
HIC-ligands 3%, 6% and 7%, respectively, of the initial amount of
virus were detected in the flow through fraction. However, the
overall material balances for the MVA-BN.RTM. virus particles could
not be closed and relative amounts of virus detected in the product
fraction ranged from 55% (ether) to 88% (PPG). For phenyl, butyl
and hexyl ligands 84%, 67% and 63%, respectively, of the initial
amount of virus were measured in the product fraction.
The fraction of un-adsorbed DNA varied for the tested HIC-resins
with ether (75%), PPG (64%), phenyl (58%), butyl (48%) and hexyl
(53%; FIG. 1). The amount of co-eluted DNA with virus particles was
for the different HIC-ligands as ether (29%), PPG (13%), phenyl
(19%) and for butyl and hexyl 4%. Here, an increase in
hydrophobicity with growing n-alkyl chain length (Queiroz et al.
2001) lead to an elevated portion of strong bound DNA, resulting in
a reduced overall recovery of DNA. For the more hydrophobic ligands
like butyl and hexyl 48% and 43% of the initial DNA content could
not be accounted for in the material balances. Strong bound DNA
were presumably removed from the HIC-resins during the regeneration
step. The hydrophobic character as confirmed in these experiments
is frequently exploited for the purification of plasmid DNA (Diogo
et al. 2001; Diogo et al. 2005; Freitas et al. 2009; Iuliano et al.
2002). These applications benefit from the relatively high
hydrophobicity of genomic DNA due to the exposure of the
hydrophobic bases, compared to plasmid DNA molecules, where the
majority of the bases are shielded inside the double helix (Freitas
et al. 2009). The presented results clearly reveals that the
hydrophobic character of free DNA from the MVA-BN.RTM. cultivation
broth can be utilized to remove residual DNA from MVA-BN.RTM. virus
particles after pseudo-affinity chromatography.
Proteins were heavily adsorbed to all tested HIC-resins under the
tested conditions. Except for the ether ligand, were 2% of the
initial protein content did not adsorb to the resin, no proteins
were determined in the flow through for all other HIC-materials.
The applied elution conditions in absence of ammonium sulfate, was
not sufficient to desorb the proteins from the HIC-resins. The
amount of total protein in the product fraction ranged from the
detection limit (butyl, hexyl) to 2% (PPG). The product fractions
of the ether and phenyl HIC-ligands contained 1% total protein. The
majority of remaining proteins on the matrix were removed from the
HIC-adsorbers during the harsh regeneration procedure. Any effects
on dynamic capacity losses have not been observed within the tested
range during the studies. However, if HIC adsorbers are applied as
an orthogonal purification step to the pseudo-affinity membrane
adsorbers, the majority of proteins are already removed and the
overall capacity of the HIC-resins will not be significantly
affected by the remaining protein load.
The high MVA-BN.RTM. recovery and DNA depletion of the PPG and
phenyl HIC resins lead to the selection of these resins to explore
their performance for a MVA-BN.RTM. vaccine downstream process in
combination with an upstream pseudo-affinity chromatography.
Studies Combining Pseudo-Affinity MA and HIC
Table 3 illustrates the amount of MVA-BN.RTM. virus particles and
DNA in the product fraction relative to the loaded sample. These
experiments were conducted with 2 different batches of MVA-BN.RTM.
virus (batch A and B) under different buffer conditions. Here,
virus particles were adsorbed and eluted from the chromatography
materials via potassium phosphate or citric acid buffers containing
ammonium sulfate according to the respective studies. The applied
chromatography media were sulfated cellulose- and heparin-MA
(pseudo-affinity MA) and the HIC-phenyl and HIC-PPG resins. Studies
conducted with batch A involved any possible combination of the two
different pseudo-affinity and HIC adsorption media (Table 3).
Table 3: Purification of two different batches (A and B) of
MVA-BN.RTM. virus particles by a sequential combination of
pseudo-affinity membrane adsorbers (sulfated cellulose (SC-MA) and
heparin (heparin-MA; gray highlighted)) and 1 ml hydrophobic
interaction chromatography columns (Phenyl and PPG). Relative
amounts (mean and standard deviation of triplicates) for
MVA-BN.RTM. (ELISA), dsDNA content (Quant-iT.RTM. PicoGreen.RTM.
assay) were calculated based on the starting material of the
homogenized and clarified virus broth. Total DNA amounts labeled by
a star were determined by the Threshold system in place of the
Quant-iT.RTM. PicoGreen.RTM. assay. The adsorption areas of the
SC-MA and heparin-MA were 75 cm2 and 225 cm.sup.2, respectively.
Pseudo-affinity equilibration and wash buffer was 100 mM citric
acid, pH 7.4 or 50 mM potassium phosphate buffer, pH 7.4 as stated
in the table, the pseudo-affinity elution buffer corresponded the
HIC-adsorption buffer (1.7 M (NH.sub.4).sub.2SO.sub.4, pH 7.4) and
the HIC elution buffers were 50 mM K.sub.2HPO.sub.4, pH7.4 or 100
mM citric acid, pH 7.4. Individual chromatographic runs were done
in triplicates from which the means and standard deviations were
calculated.
TABLE-US-00003 TABLE 3 Recoveries in Product Fraction Batch B Batch
A MVA-BN .RTM. Total MVA-BN .RTM. [%] Total DNA [%] [%] DNA [%]
Chromatography Citric Citric Citric Citric Medium K.sub.2HPO.sub.4
acid K.sub.2HPO.sub.4 acid acid acid SC-MA 73 .+-. 1.7 75 .+-. 1.6
5.8 .+-. 3.9 4.9 .+-. 0.6 81 .+-. 3.1 10 .+-. 0.4 HIC-Phenyl 76
.+-. 0.5 74 .+-. 5.1 .sup. 0.9 .+-. 0.4.sup.b .sup. 0.2 .+-.
0.0.sup.b 94 .+-. 1.1 5.6 .+-. 1.4 Overall recovery 55 56 0.04 0.01
76 0.6 Heparin-MA 68 .+-. 4.2 68 .+-. 0.6 12 .+-. 4.1 20 .+-. 0.7
62 .+-. 1.7 19 .+-. 2.8 HIC-Phenyl 73 .+-. 1.1 76 .+-. 1.9 .sup.
0.3 .+-. 0.2.sup.b .sup. 0.3 .+-. 0.0.sup.b 71 .+-. 4.1 13 .+-. 1.9
Overall recovery 50 50 0.04 0.06 44 2.5 SC-MA 77 .+-. 5.6 71 .+-.
2.7 2.0 .+-. 0.6 4.2 .+-. 0.6 n. d. n. d. HIC-PPG 64 .+-. 1.8 62
.+-. 1.7 LOQ.sup.a LOQ.sup.a n. d. n. d. Overall recovery 49 44
LOQ.sup.a LOQ.sup.a n. d. n. d. Heparin-MA 71 .+-. 2.4 59 .+-. 2.8
14 .+-. 0.5 20 .+-. 0.5 n. d. n. d. HIC-PPG 47 .+-. 1.4 60 .+-. 2.6
LOQ.sup.a LOQ.sup.a n. d. n. d. Overall recovery 33 35 LOQ.sup.a
LOQ.sup.a n. d. n. d. .sup.alimit of quantification, total protein
concentration of all samples has been below the quantification
limit; .sup.bdetermined via DNA Threshold assay
Final desorptions of the MVA-BN.RTM. product were done for all
studies with potassium phosphate and citric acid buffers as
described above.
Potential batch to batch variations were briefly explored by the
application of a second batch (batch B) of MVA-BN.RTM. virus
particles. Combinations with the HIC-PPG columns were not carried
out on grounds of the low virus recoveries for the studies with
batch A. Furthermore, final desorptions were done only with citric
acid buffer as no differences between the potassium phosphate and
citric acid buffer was observed in the initial studies and citric
acid may be beneficial to reduce potential virus aggregations due
to the high negative charge at neutral pH. The bulk of MVA-BN.RTM.
virus in the product fraction after SC-MA chromatography ranged for
experiments with potassium phosphate and citric acid from 73% to
77% and 75% to 71%, respectively. The amount of total DNA varied
for the potassium phosphate and citric acid experiments from 5.8%
to 2.0% and 4.9% to 4.2%, respectively. Hence, no significant
differences between the individual set of experiments were
encountered. However, virus yields were improved compared to
previous reports (65%; (Wolff et al. 2009) as already discussed.
DNA depletions were comparable to the previously reported values
(Wolff et al. 2009).
Observations from the chromatographic performance of sulfated
cellulose chromatography media like SC-MA or bead based sulfated
cellulose (Cellufine.RTM. sulfate) for cell culture-derived
influenza virus particles (Opitz et al. 2009) and MVA-BN.RTM.
(Wolff et al. 2009) supporting the described results. The quantity
of MVA-BN.RTM. virus in the product fraction after heparin-MA
chromatography ranged for the experiments with potassium phosphate
and citric acid from 68% to 71% and 59% to 68%, respectively. The
amount of total DNA varied for the potassium phosphate experiments
from 12% to 14% and for both sets of the citric acid experiments
20% were co-eluted with the product.
Virus recoveries after loading the homogenized and clarified
harvest onto the HIC-PPG and HIC-phenyl columns differed
significantly from the recoveries after subjecting the
pseudo-affinity chromatography processed samples over the same HIC
columns. The MVA-BN.RTM. virus recoveries for the homogenized
harvest were 88% and 84% for the HIC-PPG and HIC-phenyl column,
respectively. On the contrary, average virus recoveries for the
pseudo-affinity chromatography purified samples achieved over all
four HIC-PPG and HIC-phenyl experimental series were 58% and 75%,
respectively. The increased losses are expected due to the
differences in sample load and here in particular due to the
heavily reduced protein load after pseudo-affinity chromatography,
which could influence the adsorption behavior of the remaining
virus particles.
As expected from the results of the individual unit operations, the
buffer systems did not impact heavily the overall virus recoveries.
Focusing on the citric acid buffered experiments optimal virus
yields were accomplished with the SC-MA/HIC-phenyl combination
(56%) followed by the heparin-MA/HIC-phenyl (50%), SC-MA/HIC-PPG
(44%) and the heparin-MA/HIC-PPG (35%; Tab. 3). Due to the low
overall virus recoveries for the HIC-PPG combinations residual DNA
levels were only tested via the PicoGreen.RTM. assay and not
further characterized via the Threshold assay system. Final DNA
amounts in the product fractions varied for the SC-MA/HIC-phenyl
combination insignificantly between 0.04% and 0.01% of the starting
material (Threshold assay, Tab. 3).
However, initial tests exploring batch to batch variations by
repeating some of the experiments with batch B of homogenized and
clarified harvest resulted in an increased residual DNA content in
the product fraction in particular after the HIC-phenyl
chromatography. The DNA content in the final product fraction was
for the SC-MA/HIC-phenyl and the heparin-MA/HIC-phenyl combination
using virus batch B 0.6% and 2.5% (Tab. 3), respectively. While the
DNA content after the pseudo-affinity chromatography using the
heparin-MA was comparable, for the SC-MA there was a two-fold
increase. Main differences arised from the HIC-phenyl step,
resulting in a 30 to 40-fold increase of the final DNA content in
batch B compared to batch A (Tab. 3).
Absolute amounts of total DNA were higher in the virus harvest for
batch A than for batch B. Hence, it is not likely that capacity
limitations of the HIC-adsorber could have lead to increasing
residual DNA in the product fraction from batch B. Structural
changes on the DNA-molecules may lead to these batch to batch
variations. The integrity of DNA molecules during the production
process is mainly susceptible to cellular nucleases and shear,
leading to fragmentation or structural changes. The activity and
amount of free cellular nucleases depends on the host cell
viability during the final stages of the cultivation, which
frequently varies. Shear stress should not vary heavily during the
production process in the bioreactor. However, during the
harvesting and clearance filtration this could potentially vary and
shear induced DNA fragmentation is commonly known and has been
described in several publications (Dancis 1978; Triyoso and Good
1999).
Overall virus yields varied between the two tested chromatographic
combinations. For the SC-MA/HIC-phenyl combination using citric
acid containing buffers the virus yield was 56% (batch A) and 76%
(batch B) and for the heparin-MA/HIC-phenyl arrangement 50% (batch
A) and 44% (batch B). For the heparin-MA/HIC-phenyl downstream
process the product yields from both unit operations (batch B) were
slightly reduced leading to an overall reduction of 6% compared to
batch A. On the other hand, both unit operations of the
SC-MA/HIC-phenyl set up resulted in significant increased virus
recoveries, leading to approximately 20% increased yield. The small
variations between the different buffer systems and upstream
applied pseudo-affinity MA for batch A (50% to 56%) compared to the
virus recovery of 76% and 44% for batch B leads to the conclusion
that the performance of both unit operations depict a noteworthy
batch to batch variation which needs to be further explored for a
routine application of the downstream process for MVA-BN.RTM.
vaccine products. However, batch to batch variations of
biotechnological products are common and need to be further
addressed in process stability evaluations.
Protein concentrations were after both tested combinations of
pseudo-affinity and HIC-phenyl chromatography purifications below
the quantification range of 25 .mu.g/ml total protein (FIG. 2).
After 10 fold concentrations (lyophilization and buffer adaptation)
of representative HIC chromatography product fractions the limit
for the quantification range was still not reached. The final
protein concentration after the characterized combined purification
steps was below 25 .mu.g per dose.
Optimization of Ammonium Sulfate Concentration
The main function of the HIC was the further reduction of the DNA
contamination. This could be done in a positive or negative
adsorption mode or alternatively, via a differential elution of
virus particles and DNA. The potential applicability of HIC-resins
for this task was clearly demonstrated by the combination of the
pseudo-affinity MA and the HIC-phenyl resins (FIG. 3). Following
studies focused for the most promising HIC-ligand (phenyl) on the
reduction of the required ammonium sulfate concentration to promote
the adsorption of virus particles or DNA. At the concentration of
0.45 M ammonium sulfate 95% of the DNA and 92% MVA-BN.RTM. virus
particles did not adsorb to the HIC-phenyl resin. Increasing
ammonium sulfate concentrations led to a sudden increase of DNA
adsorption of approximately 40% which was constant over the range
of tested ammonium sulfate concentrations (0.6 M to 1.7 M).
The amount of DNA in the product fraction ranged from 10% to 20%.
Ammonium sulfate concentrations larger than 0.45 M resulted in
steady increasing virus adsorption. At 0.6 M, 0.85 M, 1.0 M, 1.25
M, 1.5 M and 1.7 M ammonium sulfate about 43%, 58%, 63%, 77%, 85%
and 85%, respectively, MVA-BN.RTM. virus particles were adsorbed
and found subsequently in the product fraction. After 1.5 M
ammonium sulfate no virus particles were detected in the flow
through fraction. The DNA content in the eluted product fractions
did not vary significantly at salt concentrations applicable for
virus adsorption and can therefore be neglected for the selection
of the optimal ammonium sulfate concentration of the adsorption
buffer. The obtained results also clearly indicate that a
differential elution of virus particles and DNA can not be achieved
by a partial reduction of the ammonium sulfate concentration during
the elution step. However, only roughly 40% of the DNA did adsorb
to the HIC-phenyl resin at relevant ammonium sulfate
concentrations, from which approximately 20% could not be eluted
under the applied conditions for virus elution. Hence, the HIC
phenyl resin represents a potential tool for a further DNA
reduction by nearly 80%. The optimal salt concentration was judged
based on the lowest possible ammonium sulfate concentration
allowing complete virus adsorption (1.5 M ammonium sulfate).
However, for reasons of process stability 1.7 M ammonium sulfate
were used for the following studies. Comparing the resulting
ammonium sulfate concentration with literature shows that for many
different biomolecules ammonium sulfate concentrations of 1.5 to
2.0 M are sufficient for high yield recoveries without denaturation
(Kato et al. 2004). However, especially the denaturation aspect
depends mainly on the target and contaminating molecules.
Virus Infectivity after Downstream Processing
The effect of the described downstream process and especially the
high ammonium sulfate concentration on the virus infectivity was
tested via the TCID.sub.50 assay. Therefore, representative samples
were selected after a SC-MA or heparin-MA and HIC-phenyl
combination, with adsorption buffers containing 1.7 M ammonium
sulfate. Each product fraction of the triplicate chromatographic
runs were assayed and the average TCID.sub.50 determined. The
initial TCID.sub.50 (blank for this particular assays) of the
homogenized and clarified harvest was 4.2.times.10.sup.7 for this
particular experiment. The average TCID.sub.50 from the final
product fractions of the SC-MA/HIC-phenyl, and
heparin-MA/HIC-phenyl downstream processes were 1.7.times.10.sup.7
and 1.6.times.10.sup.7 TCID.sub.50, respectively. Hence, the entire
process including HIC-adsorption, led to an approximate reduction
of the TCID.sub.50 of 0.3 log units. The overall relative losses of
the virus particles based on the ELISA quantification of the
initially loaded sample were on average for both processes 47%
(FIG. 2), which corresponds to approximately 0.3 log units from the
TCID.sub.50. Therefore, it can be concluded that losses on virus
infectivity were not significantly impacted by the high
concentration of ammonium sulfate.
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